What is ICD-11? A Complete Guide to the WHO Classification System
Everything you need to know about the International Classification of Diseases, 11th Revision — from its structure and code format to real-world adoption and clinical use.
ICD-11 (International Classification of Diseases, 11th Revision) is the global standard for recording and classifying diseases, injuries, causes of death, and other health conditions. It is developed and maintained by the World Health Organization (WHO).
Officially released in June 2018 and endorsed by the World Health Assembly in May 2019, ICD-11 became effective for member state reporting on January 1, 2022. It represents the first major revision of the classification in over 30 years, replacing ICD-10 which was adopted in 1990.
ICD-11 was designed from the ground up for the digital age. Unlike ICD-10, which was originally published as printed volumes, ICD-11 is a fully electronic classification with built-in support for APIs, persistent URIs, and integration with modern health information systems.
Key Features of ICD-11
Digital-First Design
ICD-11 is natively electronic. Every entity has a stable URI (Uniform Resource Identifier), and the WHO provides a free coding tool, browser, and API. This makes ICD-11 easy to integrate into electronic health records (EHRs), clinical decision support systems, and health information exchanges.
Post-Coordination & Extension Codes
Instead of creating a unique code for every possible clinical detail, ICD-11 uses post-coordination: a stem code combined with one or more extension codes. For example, a stem code for diabetes can be combined with extension codes for severity, anatomical site, or causality. This enables far more precise coding without exponentially growing the code set.
Foundation Layer
ICD-11 is built on a foundation component — a comprehensive knowledge base of over 80,000 medical entities. From this foundation, multiple statistical linearizations can be derived. The main one used for mortality and morbidity statistics (MMS) contains approximately 17,000 categories, but specialized linearizations for primary care, dermatology, or mental health can also be generated.
Improved Clinical Coverage
ICD-11 expands coverage with 28 chapters (up from 22 in ICD-10), adding dedicated chapters for diseases of the immune system, sleep-wake disorders, conditions related to sexual health, and traditional medicine conditions. Many existing chapters were restructured to reflect current medical knowledge.
ICD-11 Code Structure
ICD-11 uses an alphanumeric coding scheme that differs significantly from ICD-10. Understanding this structure is essential for anyone working with the new classification.
Stem Codes
Stem codes are the primary diagnostic codes in ICD-11. They follow a pattern of one or more letters followed by digits, with an optional dot separator. The first character identifies the chapter.
| Code | Description | Chapter |
|---|---|---|
| 5A11 | Type 2 diabetes mellitus | 5 — Endocrine diseases |
| BA00 | Essential hypertension | 11 — Circulatory system diseases |
| CA40.0 | Acute lymphoblastic leukaemia | 2 — Neoplasms |
| MG30 | Chronic pain | 21 — Symptoms & signs |
Extension Codes (Chapter X)
Extension codes begin with the letter “X” and cannot be used alone. They are always paired with a stem code using the “&” operator to add clinical detail such as severity, laterality, anatomical site, or causality.
For example: 5A11 & XS9T represents Type 2 diabetes mellitus with a severity extension. Learn more about how this works on the extension codes guide.
ICD-11 is organized into 28 chapters, numbered 1–28 (including Chapter X for extension codes and the supplementary chapter for traditional medicine). You can browse all ICD-11 chapters in our code directory.
Who Uses ICD-11?
ICD-11 is used by governments, healthcare systems, researchers, and international organizations worldwide. Its primary use cases include:
- Mortality reporting: WHO member states use ICD-11 to report cause-of-death statistics, enabling global health monitoring and epidemiological research.
- Morbidity statistics: Hospitals and health systems use ICD-11 to classify and report diagnoses for public health surveillance and healthcare planning.
- Clinical documentation: ICD-11's post-coordination allows clinicians to capture more detailed diagnostic information than previous versions.
- Research: The expanded code set and digital-first design make ICD-11 particularly useful for clinical research, health economics, and population health studies.
Countries including China, Saudi Arabia, Kazakhstan, and several others have begun implementing ICD-11, with many more planning their transition. The WHO provides implementation guidance and training materials to support national adoption.
ICD-11 and Clinical Coding
In clinical practice, ICD-11 codes are assigned to patient encounters to document diagnoses, justify treatments, support reimbursement claims, and enable population health analytics. The coding process typically involves:
- Reviewing the clinical documentation (progress notes, discharge summaries, lab results)
- Identifying all relevant diagnoses and conditions mentioned in the documentation
- Selecting the most specific ICD-11 stem code that matches each condition
- Adding extension codes where appropriate to capture severity, anatomical detail, or causality
- Validating the code combinations for clinical accuracy
Modern AI-powered coding tools can automate much of this process, analyzing clinical text and suggesting appropriate ICD codes. The AutoICD API supports both ICD-10-CM and ICD-11 coding from free-text clinical notes.
Explore ICD-11
Frequently Asked Questions
What does ICD-11 stand for?
ICD-11 stands for the International Classification of Diseases, 11th Revision. It is the global standard for recording, reporting, and classifying diseases, health conditions, and causes of death, maintained by the World Health Organization (WHO).
When was ICD-11 released?
ICD-11 was officially released by the WHO in June 2018 and endorsed by the World Health Assembly in May 2019. It became effective for member state reporting on January 1, 2022.
How many codes does ICD-11 have?
The ICD-11 Mortality and Morbidity Statistics (MMS) linearization contains approximately 17,000 diagnostic categories. However, through post-coordination with extension codes, ICD-11 can represent far more clinical concepts than the ~74,000 codes in ICD-10-CM.
Has the United States adopted ICD-11?
As of 2024, the United States has not yet adopted ICD-11 for clinical billing purposes. The US continues to use ICD-10-CM for diagnosis coding. However, ICD-11 is being used for mortality reporting and research purposes globally, and US adoption planning is underway.
What is the difference between ICD-11 and ICD-10?
ICD-11 introduces a digital-first design with built-in APIs and URIs, post-coordination through extension codes, 28 chapters (vs. 22 in ICD-10), new chapters for conditions like sleep-wake disorders and sexual health, and a foundation layer that supports multiple statistical linearizations.
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