ICD-10-CM is organized into 21 chapters, sequenced by the first letter(s) of the code. Always begin in the Alphabetic Index, then confirm the full code in the Tabular List.
| # | Chapter | Range |
|---|---|---|
| 1 | Certain infectious & parasitic diseases | A00–B99 |
| 2 | Neoplasms | C00–D49 |
| 3 | Blood, blood-forming organs & immune disorders | D50–D89 |
| 4 | Endocrine, nutritional & metabolic diseases | E00–E89 |
| 5 | Mental, behavioral & neurodevelopmental disorders | F01–F99 |
| 6 | Nervous system | G00–G99 |
| 7 | Eye & adnexa | H00–H59 |
| 8 | Ear & mastoid process | H60–H95 |
| 9 | Circulatory system | I00–I99 |
| 10 | Respiratory system | J00–J99 |
| 11 | Digestive system | K00–K95 |
| 12 | Skin & subcutaneous tissue | L00–L99 |
| 13 | Musculoskeletal & connective tissue | M00–M99 |
| 14 | Genitourinary system | N00–N99 |
| 15 | Pregnancy, childbirth & the puerperium | O00–O9A |
| 16 | Certain conditions originating in the perinatal period | P00–P96 |
| 17 | Congenital malformations & chromosomal abnormalities | Q00–Q99 |
| 18 | Symptoms, signs & abnormal findings | R00–R99 |
| 19 | Injury, poisoning & external consequences | S00–T88 |
| 20 | External causes of morbidity | V00–Y99 |
| 21 | Factors influencing health status (Z codes) | Z00–Z99 |
Note: ranges follow the current code set and update annually — always verify in your current-year ICD-10-CM manual. Always begin in the Alphabetic Index, then confirm the full code in the Tabular List.
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