ICD-10 vs ICD-11: diagnostic categories, chapters and key changes in the WHO classification

What is the ICD and what is it for?

The International Statistical Classification of Diseases and Related Health Problems (ICD) is the WHO standard for coding diagnoses, causes of death, medical procedures and contacts with health services. It is used in medical records, health reporting, health statistics and epidemiological research worldwide. The classification covers all areas of medicine – not just psychiatry, but also infectious diseases, cancer, cardiology, neurology, injuries, rare diseases and hundreds of other fields.^[1,2]

The ICD-10 classification has been in use since 1994 in most countries. ICD-11, approved by WHO in 2019, entered into force globally on 1 January 2022, with a transition period. ICD-11 was designed from the outset for digital use – with URIs for concepts, API access, coding tools and the ability to integrate with electronic health records.^[3] The difference between ICD-10 and ICD-11 therefore concerns both substantive content and the entire information architecture.

ICD-10 – 22 chapters of disease classification

ICD-10 has 22 chapters, labelled with Roman numerals. Some chapters group diseases by organ system (circulatory, respiratory, digestive), others are cross-sectional (infectious, neoplasms, injuries) or administrative (unclassified symptoms, health factors, special codes). Codes have the format letter + two digits, optionally with a digit after the decimal point for subtypes: e.g. F33.1 = recurrent depressive disorder, current episode moderate.^[2]

ICD-11 – new classification architecture

ICD-11 uses alphanumeric codes composed of combinations of digits and letters, for example 6A70 for depressive episode instead of the ICD-10 code F32. The version of the classification used for mortality and morbidity statistics is called ICD-11 MMS (Mortality and Morbidity Statistics). It includes 26 main chapters, a section for functioning assessment (V), and extension codes (X). The classification contains more than 55,000 codes referring to diseases, injuries and causes of death.^[3]

Structural differences: ICD-10 vs ICD-11

The table below sets out the key technical and organisational differences between the two classifications.^[3,5,7]

New chapters in ICD-11

Four areas that were absent or scattered in ICD-10 now have dedicated chapters in ICD-11.^[3,5]

Diseases of the immune system – Chapter 04

In ICD-10, diseases of the immune system were grouped together with blood diseases in Chapter III. ICD-11 separates diseases of the immune system (4A00–4B4Z) into their own fourth chapter. This better reflects developments in clinical immunology and the need to describe autoimmune, allergic and immunodeficiency conditions more precisely.

Sleep-wake disorders – Chapter 07

In ICD-10 sleep disorders were scattered: non-organic sleep disorders in the psychiatric chapter (F51), others in neurology and elsewhere. ICD-11 creates a dedicated Chapter 07 (Sleep-wake disorders). Sleep is no longer treated solely as a symptom of another psychiatric or neurological condition; it is an independent classification area.

Conditions related to sexual health – Chapter 17

ICD-11 introduces a dedicated Chapter 17. Some conditions previously placed in mental and behavioural disorders or in the genitourinary chapter have been moved here. The most widely discussed example is the relocation of gender incongruence out of the mental disorders chapter.

Functioning section (V) and extension codes (X)

Section V (VA00–VC50) enables an in-depth assessment of patient functioning. Section X (XA00–XZ9Z) contains extension codes that specify severity, cause, laterality, timing, circumstance of diagnosis and many other clinical dimensions – without needing a separate main code for every combination.^[5]

Coding in ICD-11: stem codes, extension codes and postcoordination

In ICD-10, a diagnosis was typically one code. Exceptions existed (the dagger-asterisk convention for aetiology and manifestation), but there was no general mechanism for combining codes. ICD-11 introduces code clusters as a systemic element of the classification.^[3,5]

Stem codes are the basic codes – diagnoses that can be assigned on their own. Extension codes (section X) cannot be used alone; they describe additional dimensions such as severity, location, cause, laterality or stage of course. Postcoordination is the combination of a stem code with extension codes or with other stem codes to give a more precise description of the clinical condition.

Example: in ICD-10 an injury often required one code for the injury and another for the external cause, without a way to describe the accompanying circumstances in a single code.

ICD-11 as a digital system

WHO provides a full suite of digital tools for ICD-11:^[5,7]

• ICD-11 Browser – hierarchical browsing with concept search
• Coding Tool – interactive clinical coding tool (including postcoordination)
• ICD-API – programmatic REST API access, with a URI for every concept
• Embedded Coding Tool – version for integration with HIS/EHR systems
• Reference Guide – full instructions for using ICD-11 in health information systems
• ICD-10/ICD-11 mapping tables – official conversion tables available via the ICD-11 Browser

With ICD-10, users typically worked with the classification as a list of codes. With ICD-11, the classification functions as a digital knowledge base: every concept has a unique URI, is accessible via API, searchable in multiple languages, and can be linked programmatically to electronic health records.

Mental disorders in ICD-11 vs ICD-10 – overview

The chapter on mental disorders in ICD-11 is no longer titled "Mental and behavioural disorders" (as in ICD-10), but "Mental, behavioural or neurodevelopmental disorders." This reflects structural rebuilding: the explicit inclusion of neurodevelopmental disorders (ASD, ADHD) and changed logic for many categories.^[4,6]

Reed and colleagues describe ICD-11's shift in mental health from fixed type categories towards dimensional description: severity, course, symptom profile and functioning. This does not abandon diagnostic categories – they remain the basis of classification – but adds clinically useful specifiers.^[4]

Personality disorders: the end of old types

The change in personality disorders is one of the most important shifts between ICD-10 and ICD-11. In ICD-10, diagnosis was based mainly on assigning the patient to one of several defined personality types, such as paranoid, schizoid, dissocial, emotionally unstable borderline type, anankastic or dependent personality disorder. The problem with this model was that many clinical pictures did not fit neatly into a single category. Features of several types often occurred at the same time, and in clinical practice personality disorder not otherwise specified was used relatively often.^[4,6]

ICD-11 abandons the old personality types as the main diagnostic categories. Personality disorder is coded as 6D10, and diagnosis is more dimensional and descriptive. The process can be understood in three steps: first, whether a personality disorder is present at all; second, its severity as mild (6D10.0), moderate (6D10.1) or severe (6D10.2); third, the dominant personality trait domains (6D11) can be specified and, where clinically justified, the borderline pattern qualifier (6D11.5) can be added.

This means that ICD-11 replaces the question "what type of personality disorder is this?" with a more clinical description: whether personality disorder is present, how strongly it disrupts the patient's functioning, and which traits dominate the clinical picture. The key issue is a persistent pattern of difficulties in self-functioning and interpersonal functioning. Severity is then assessed, and only afterwards are dominant traits described, such as negative affectivity, detachment, dissociality, disinhibition and anankastia. The borderline pattern remains in ICD-11, but it does not function as a separate main personality disorder diagnosis; it is an additional qualifier.

It is important to stress, however, that former ICD-10 diagnoses do not translate mechanically into ICD-11 trait-domain descriptions. The new model requires a renewed clinical assessment covering severity, self-functioning, interpersonal functioning and dominant personality traits. ICD-11 is therefore not merely a change of names, but a substantial change in how personality disorders are conceptualised. A detailed discussion of the new model, severity levels and diagnostic criteria is available in a separate article: Personality disorders in ICD-11.

Schizophrenia: the end of classical subtypes

One of the more important ICD-11 changes is the removal of classical schizophrenia subtypes. In ICD-10, schizophrenia was divided into several categories, including paranoid schizophrenia (F20.0), hebephrenic schizophrenia (F20.1), catatonic schizophrenia (F20.2), undifferentiated schizophrenia (F20.3), residual schizophrenia (F20.5) and simple schizophrenia (F20.6). The problem with this model was that these subtypes were often unstable over time. The same patient could present a picture dominated by paranoid symptoms in one episode and a more residual, disorganised or negative-symptom picture in another. In practice, subtypes more often described a cross-section of the current clinical picture than the actual course of the disorder.

ICD-11 moves away from this way of classifying schizophrenia. Schizophrenia functions as a single diagnostic category with code 6A20, while the course of the disorder, current clinical status and dominant symptom domains become more important.^[4,6]

Removing subtypes does not mean that paranoid, catatonic, disorganised or negative symptoms have lost clinical importance. ICD-11 describes them more flexibly, through symptom domains and course specifiers rather than fixed diagnostic subtypes. The change concerning catatonia is especially important. It is no longer treated only as a form of schizophrenia, but as a separate category (6A41) that may occur in schizophrenia, mood disorders, central nervous system diseases and other clinical conditions.

A detailed discussion of this change is available in a separate article: Schizophrenia diagnosis in ICD-11.

Neurodevelopmental disorders

ICD-11 separates a clear group of neurodevelopmental disorders (6A00–6A0Z). This better reflects the contemporary understanding of these disorders as conditions that begin in the developmental period and affect cognitive, social, emotional, communicative and adaptive functioning. In ICD-10, autism spectrum disorders were located among pervasive developmental disorders (F84), whereas ADHD was classified as hyperkinetic disorder (F90) among disorders with onset usually occurring in childhood and adolescence.^[4,6]

Autism spectrum: one spectrum instead of separate types

ICD-10 included separate diagnoses such as childhood autism, atypical autism and Asperger syndrome. ICD-11 abandons this division and places these clinical pictures within one category: autism spectrum disorder (6A02). Instead of assigning a person to one of the historical categories, ICD-11 allows a more precise description of functioning, especially in relation to intellectual development and functional language.

A person who could have received an Asperger syndrome diagnosis in ICD-10 would most often be described in ICD-11 as a person with autism spectrum disorder without disorder of intellectual development and without disorder of functional language, or with only mild impairment in this area. This change better captures the fact that autism is not a set of sharply separated categories, but a spectrum of different functioning profiles. A detailed discussion of this change is available in a separate article: Autism spectrum in ICD-11.

ADHD: from hyperkinetic disorders to a neurodevelopmental disorder

ICD-10 used the category of hyperkinetic disorders (F90). It was placed among disorders with onset usually occurring in childhood and adolescence. ICD-11 uses the name ADHD and classifies this diagnosis in the neurodevelopmental disorders group as 6A05.

This change is consistent with the contemporary understanding of ADHD as a neurodevelopmental disorder involving difficulties with inattention, excessive activity and impulsivity. These symptoms may begin in childhood, but in some people they also persist into adulthood. ICD-11 also allows the clinical presentation of ADHD to be specified: predominantly inattentive, predominantly hyperactive-impulsive or combined. A detailed discussion is available in a separate article: ADHD in adults.

PTSD and complex PTSD (CPTSD)

In ICD-10, PTSD was coded as F43.1 and referred to the classic post-traumatic reaction. The classification did not include a separate category for more complex, multidimensional consequences of prolonged or repeated trauma. ICD-11 introduces an important distinction between PTSD (6B40) and complex PTSD, or CPTSD (6B41).^[4,6]

In ICD-11, PTSD and CPTSD are mutually exclusive diagnoses. This means they should not be diagnosed at the same time. If CPTSD diagnostic requirements are met, the diagnosis includes the core symptoms of PTSD but also captures broader difficulties in emotion regulation, self-concept and interpersonal relationships.

The distinction between PTSD and CPTSD has important clinical and therapeutic implications. In PTSD, treatment focuses primarily on symptoms linked to the traumatic experience, such as re-experiencing, avoidance and persistent sense of threat. In CPTSD, broader intervention is usually needed, including emotional stabilisation, rebuilding self-concept and work on interpersonal relationships.

A detailed discussion is available in a separate article: Complex PTSD (CPTSD) in ICD-11.

New and significantly reorganised psychiatric categories in ICD-11

ICD-11 introduces several categories that did not function as separate diagnoses in ICD-10 or were described in a less precise way. These changes involve both new diagnostic entities and the reorganisation of whole groups of disorders, so that the classification better reflects contemporary understanding of clinical presentation, course and functional consequences.^[4,6]

Prolonged grief disorder (6B42)

ICD-11 separates prolonged grief disorder as a distinct diagnosis in the group of disorders specifically associated with stress. The core of the disorder is persistent longing for the deceased person or strong preoccupation with the loss, accompanied by intense emotional pain and marked impairment in functioning.

Introducing this category makes it easier to distinguish prolonged grief disorder from depressive episode, PTSD and adjustment disorder. The point is not to pathologise grief itself, but to recognise situations in which the reaction to loss remains persistent, disorganising and significantly limiting in everyday functioning. A detailed discussion is available in a separate article: Prolonged grief disorder in ICD-11.

Gaming disorder (6C51)

ICD-11 introduces gaming disorder as a diagnosis in the group of disorders due to addictive behaviours. The diagnosis concerns a pattern of gaming in which control over the behaviour is lost, gaming is given increasing priority over other activities, and gaming continues despite negative consequences.^[4]

Importantly, spending a long time playing games is not sufficient for the diagnosis. The key elements are loss of control, persistence of the pattern, other areas of life becoming subordinated to gaming, and marked impairment in personal, family, social, educational or occupational functioning. A detailed discussion is available in a separate article: Gaming disorder in ICD-11.

Compulsive sexual behaviour disorder (6C72)

ICD-11 introduces compulsive sexual behaviour disorder in the impulse-control disorders group. The diagnosis concerns a persistent pattern of difficulty controlling intense sexual impulses, fantasies or behaviours, leading to distress or impaired functioning.

It is not a simple equivalent of the idea of "sex addiction." In ICD-11, what matters is not the frequency of sexual activity itself or a moral judgement of the behaviour, but loss of control, repetition of the pattern and real clinical, social or functional consequences.

Eating disorders: ARFID and binge-eating disorder

ICD-11 broadens the eating and feeding disorders group. Alongside anorexia nervosa and bulimia nervosa, it introduces more precise categories, including binge-eating disorder and ARFID (avoidant-restrictive food intake disorder).

In binge-eating disorder, the key feature is recurrent binge-eating episodes that are not accompanied by regular compensatory behaviours typical of bulimia, such as vomiting, while shame and guilt dominate after the episode. ARFID describes a pattern of avoiding or restricting food intake that does not result from fear of weight gain or body-image disturbance, but may lead to nutritional deficiencies, weight loss, dependence on supplementation or significant functional impairment.

OCD and related disorders – separate group

In ICD-10, obsessive-compulsive disorder (F42) was located in the broad group of neurotic, stress-related and somatoform disorders. ICD-11 creates a separate group of obsessive-compulsive or related disorders (6B20–6B25).

This group includes OCD, body dysmorphic disorder, hoarding disorder and body-focused repetitive behaviour disorders, among others. The change is organisationally important because it separates OCD and related disorders from the broad historical category of "neuroses" and better reflects shared clinical mechanisms such as intrusiveness, compulsivity, repetition and difficulty controlling behaviour.

Reclassification of gender incongruence in ICD-11

In ICD-10, categories related to gender identity were located in the mental disorders chapter as F64. ICD-11 moves gender incongruence to the chapter on sexual health, where it appears, among others, under code HA60.

This change has important clinical and social meaning. It does not remove the possibility of coding health needs in this area, but it moves away from classifying gender incongruence as a mental disorder. In this way, ICD-11 preserves the ability to document health needs while reducing the stigmatising effect of the previous placement.

Dissociative disorders: new organisation

In ICD-10, dissociative and conversion disorders (F44) were part of the broad group of neurotic, stress-related and somatoform disorders. ICD-11 treats dissociative disorders (6B60–6B6Z) as a more distinct group, with greater emphasis on disturbances in the integration of identity, memory, consciousness, perception, emotion, motor control and the sense of continuity of experience.

This change organises an area that in ICD-10 was strongly tied to the historical terminology of "conversion." ICD-11 better reflects the contemporary understanding of dissociation as a phenomenon involving not only motor or sensory symptoms, but also disruptions in identity, autobiographical memory and the coherence of self-experience.

Implementation and summary

ICD-11 entered into force globally on 1 January 2022. WHO ended maintenance of ICD-10 in 2018, which means that new improvements, updates and extensions are now developed within ICD-11. The pace of implementation in individual countries depends on national decisions, IT infrastructure, reimbursement systems and staff training. WHO also provides official ICD-10/ICD-11 mappings to support gradual transition between classifications.^[7]

ICD-11 is not merely a "newer code list." It is a new architecture for describing health, diseases, injuries, causes of death, functioning and contacts with the health-care system. It preserves the basic classification function known from ICD-10, but substantially changes the organisation and description of many clinical areas.

The most important changes include, among others, describing personality disorders by severity and trait domains, abandoning classical schizophrenia subtypes, treating autism as a broad spectrum, separating complex PTSD, introducing new categories such as prolonged grief disorder, gaming disorder and compulsive sexual behaviour disorder, and creating separate chapters for sleep disorders and sexual health. At the same time, ICD-11 introduces a full digital infrastructure: extension codes, postcoordination, URI identifiers, API access and a more flexible way of connecting diagnostic information with electronic documentation.

In practice, ICD-11 is a more precise, digital and flexible classification, but also a more complex one. Its usefulness therefore depends not only on the structure of codes itself, but also on good tools, training and clear educational resources that make it easier to navigate the new system. ICD Diagnostica is an example of such a tool, supporting the process of diagnosis and differential diagnosis.

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