ICD-11

The ICD-11 is the eleventh revision of the International Classification of Diseases. It replaces the ICD-10 as the global standard for recording health information and causes of death. The ICD is developed and annually updated by the World Health Organization. Development of the ICD-11 started in 2007 and spanned over a decade of work, involving over 300 specialists from 55 countries divided into 30 work groups, with an additional 10,000 proposals from people all over the world. Following an alpha version in May 2011 and a beta draft in May 2012, a stable version of the ICD-11 was released on 18 June 2018, and officially endorsed by all WHO members during the 72nd World Health Assembly on 25 May 2019.
The ICD-11 is a large ontology consisting of about 85,000 entities, also called classes or nodes. An entity can be anything that is relevant to health care. It usually represents a disease or a pathogen, but it can also be an isolated symptom or anomaly of the body. There are also classes for reasons for contact with health services, social circumstances of the patient, and external causes of injury or death. The ICD-11 is part of the WHO-FIC, a family of medical classifications. The WHO-FIC contains the Foundation Component, which comprises all entities of the classifications endorsed by the WHO. The Foundation is the common core from which all classifications are derived. For example, the ICD-O is a derivative classification optimized for use in oncology. The primary derivative of the Foundation is called the ICD-11 MMS, and it is this system that is commonly referred to as simply "the ICD-11". MMS stands for Mortality and Morbidity Statistics. The ICD-11 is distributed under a Creative Commons BY-ND license.
The ICD-11 officially came into effect on 1 January 2022. On 14 February 2023, the WHO reported that 64 countries were "in different stages of ICD-11 implementation". In May 2024, they stated that 50 countries were either conducting or expanding implementation pilots, and that 14 countries were actively using the ICD-11. According to a JAMA article from July 2023, implementation in the United States would at minimum require 4 to 5 years.
The ICD-11 MMS can be viewed online on the WHO's website. Aside from this, the site offers two maintenance platforms: the ICD-11 Maintenance Platform, and the WHO-FIC Foundation Maintenance Platform. Users can submit evidence-based suggestions for the improvement of the WHO-FIC, i.e., the ICD-11, the ICF, and the ICHI.

Structure

WHO-FIC

The WHO Family of International Classifications, also called the WHO Family, is a suite of classifications used to describe various aspects of the health care system in a consistent manner, with a standardised terminology. The abbreviation is variously written with or without a hyphen. The WHO-FIC consists of four components: the WHO-FIC Foundation, the Reference Classifications, the Derived Classifications, and the Related Classifications. The WHO-FIC Foundation, also called the Foundation Component, represents the entire WHO-FIC universe. It is a collection of over hundred thousand entities, also called classes or nodes. Entities are anything relevant to health care. They are used to describe diseases, disorders, body parts, bodily functions, reasons for visit, medical procedures, microbes, causes of death, social circumstances of the patient, and much more.
The Foundation Component is a multidimensional collection of entities. An entity can have multiple parents and child nodes. For example, pneumonia can be categorized as a lung infection, but also as a bacterial or viral infection. Thus, the node Pneumonia has two parents: Lung infections and Certain infectious or parasitic diseases. The Pneumonia node in turn has various children, including Bacterial pneumonia and Viral pneumonia.
The Foundation Component is the common core on which all Reference and Derived Classifications are based. The WHO-FIC contains three Reference Classifications: the ICD-11 MMS, the ICF, and the ICHI. Derived Classifications are based on the three Reference Classifications, and are usually tailored for a particular specialty. For example, the ICD-O is a Derived Classification used in oncology. Each node of the Foundation has a unique entity id, which remains the same in all Reference and Derived Classifications, guaranteeing consistency. Related Classifications are complementary, and cover specialty areas not covered elsewhere in the WHO-FIC. For example, the International Classification of Nursing Practice, draws on terms from the Foundation Component, but also uses terms specific for nursing not found in the Foundation.
A classification can be represented as a tabular list, which is a "flat" hierarchical tree of categories. In this tree, all entities can only have a single parent, and therefore must be mutually exclusive of each other. Such a classification is also called a linearization.

ICD-11 MMS

The ICD-11 MMS is the main Reference Classification of the WHO-FIC, and the primary linearization of the Foundation Component. The ICD-11 MMS is commonly referred to as simply "the ICD-11". The "MMS" part was added to differentiate the ICD-11 entities in the Foundation from those in the Classification. The ICD-11 MMS does not contain all classes from the Foundation ICD-11, and also adds some classes from the ICF. MMS stands for Mortality and Morbidity Statistics. The abbreviation is variously written with or without a hyphen between 11 and MMS.
The ICD-11 MMS consists of approximately 85,000 entities. Entities can be chapters, blocks or categories. A chapter is a top level entity of the hierarchy; the MMS contains 28 of them. A block is used to group related categories or blocks together. A category can be anything that is relevant to health care. Every category has a unique, alphanumeric code called an ICD-11 code, or just ICD code. Chapters and blocks never have ICD-11 codes, and therefore cannot be diagnosed. An ICD-11 code is not the same as an entity id.
The ICD-11 MMS takes the form of a "flat" hierarchical tree. As aforementioned, the entities in this linearization can only have a single parent, and therefore must be mutually exclusive of each other. To make up for this limitation, the hierarchy of the MMS contains gray nodes. These nodes appear as children in the hierarchy, but actually have a different parent node. They originally belong to a different block or chapter, but are also listed elsewhere because of overlap. For example, Pneumonia has two parents in the Foundation: "Lung infections" and "Certain infectious or parasitic diseases". In the MMS, Pneumonia is categorized in the "Lung infections", with a gray node in "Certain infectious or parasitic diseases". The same goes for injuries, poisonings, neoplasms, and developmental anomalies, which can occur in almost any part of the body. They each have their own chapters, but their categories also have gray nodes in the chapters of the organs they affect. For instance, the blood cancers, including all forms of leukemia, are in the "Neoplasms" chapter, but they are also displayed as gray nodes in the chapter "Diseases of the blood or blood-forming organs".
The ICD-11 MMS also contains residual categories, or residual nodes. These are the "Other specified" and "Unspecified" categories. The former can be used to code conditions that do not fit with any of the more specific MMS entities, the latter can be used when necessary information may not be available in the source documentation. The ICD-11 Reference Guide advises that health care workers always aim to include the most specific level of detail possible, either with one code or multiple codes. In the ICD-11 Browser, residual nodes are displayed in a maroon color. Residual categories are not in the Foundation, and therefore do not have an entity ID. Thus, in the MMS, they are the only categories with derivative entity IDs: their IDs are the same as their parent nodes, with "/other" or "/unspecified" tagged at the end. Their ICD codes always end with Y for "Other specified" categories, or Z for "Unspecified" categories.
Codes can include 'inclusions'. These are terms or conditions which are judged important or commonly used in relation to that code.

Usage

ICD-11 is a digital-first classification that supports straightforward single-code assignment for routine use. Where additional detail is required, post-coordination allows code clusters to be created; the Browser and Coding Tool guide users through these combinations.
ICD-11 provides a REST and FHIR-compliant multilingual API and embeds a web-based Coding Tool in the Browser for everyday coding. Tooling includes search, clustering of stem and extension codes, and NLP-assisted features to reduce manual lookup and improve accuracy. ICD-11 with all its tools can be downloaded and used on local computers in Docker, or as a Windows or Linux server. Code samples facilitate integration in existing software. Documentation on the above, the ICD API and some additional tools for integration into third-party applications can be found at the ICD API home page.
The WHO has released spreadsheets that can be used to link and convert ICD-10 codes to those of the ICD-11. They can be downloaded from the ICD-11 MMS browser. Since 2017, WHO and SNOMED International are exploring ways of funding and governance in relation to formulating a bidirectional map between SNOMED CT and ICD-11. No deadlines for agreements, start of the work, or availability of any map has been communicated as of 2025.
The ICD-11 Foundation, and consequently the MMS, are updated annually, similarly to the ICD-10. Following the initial release of a stable version on 18 June 2018, the Foundation and the MMS have received seven updates as of 2025.

Chapters

Below is a table of all chapters of the ICD-11 MMS, the primary linearization of the Foundation Component.

#	Range	Chapter	#	Range	Chapter
1	1A00–1H0Z	Certain infectious or parasitic diseases	15	FA00–FC0Z	Diseases of the musculoskeletal system or connective tissue
2	2A00–2F9Z	Neoplasms	16	GA00–GC8Z	Diseases of the genitourinary system
3	3A00–3C0Z	Diseases of the blood or blood-forming organs	17	HA00–HA8Z	Conditions related to sexual health
4	4A00–4B4Z	Diseases of the immune system	18	JA00–JB6Z	Pregnancy, childbirth or the puerperium
5	5A00–5D46	Endocrine, nutritional or metabolic diseases	19	KA00–KD5Z	Certain conditions originating in the perinatal period
6	6A00–6E8Z	Mental, behavioural or neurodevelopmental disorders	20	LA00–LD9Z	Developmental anomalies
7	7A00–7B2Z	Sleep-wake disorders	21	MA00–MH2Y	Symptoms, signs or clinical findings, not elsewhere classified
8	8A00–8E7Z	Diseases of the nervous system	22	NA00–NF2Z	Injury, poisoning or certain other consequences of external causes
9	9A00–9E1Z	Diseases of the visual system	23	PA00–PL2Z	External causes of morbidity or mortality
10	AA00–AC0Z	Diseases of the ear or mastoid process	24	QA00–QF4Z	Factors influencing health status or contact with health services
11	BA00–BE2Z	Diseases of the circulatory system	25	RA00–RA26	Codes for special purposes
12	CA00–CB7Z	Diseases of the respiratory system	26	SA00–SJ3Z	Supplementary Chapter Traditional Medicine Conditions - Module I
13	DA00–DE2Z	Diseases of the digestive system	V	VA00–VC50	Supplementary section for functioning assessment
14		Diseases of the skin	X		Extension Codes

Unlike the ICD-10 codes, the ICD-11 MMS codes never contain the letters I or O, to prevent confusion with the numbers 1 and 0.