ICD (International Classification of Diseases) is a globally used system for classifying diseases and health-related problems, maintained by the World Health Organization (WHO). The ICD coding system provides alphanumeric codes to classify diseases, disorders, injuries, and other health conditions. These codes are used for various purposes, including medical billing, health statistics, and research.

The United States currently uses ICD-10 (International Classification of Diseases, Tenth Revision). Here are some ICD-10 code examples:

• C34.11 Malignant neoplasm of upper lobe, right bronchus or lung
• G43.901 Migraine, unspecified, not intractable, with status migrainosus
• S80.01XS Contusion of right knee, sequela

ICD-10-CM

The Centers for Medicare & Medicaid Services (CMS) mandates the use of ICD-10-CM (International Classification of Diseases, Tenth Revision, Clinical Modification) for medical billing and claims. In the United States, the names "ICD-10" and "ICD-10-CM" are often used interchangeably in conversation, but in information system applications these codesets are different and not interchangeable.

ICD-10-CM is a coding system used in the United States to classify and code diagnoses and procedures associated with hospital and outpatient medical services. ICD-10-CM is based on the international ICD-10 system, but it includes additional diagnosis codes and has been modified to suit the specific needs of the U.S. healthcare system, including payment, reimbursement, and epidemiological tracking.

ICD-11

ICD-11 was adopted by the World Health Assembly in 2019 and is being implemented globally. Many countries have transitioned to ICD-11 since it became available in January 2022. In the United States, ICD-10-CM/PCS remains the required standard for clinical coding and billing. Evaluation of ICD-11 adoption is ongoing, but no official transition timeline has been established as of 2026.