- Nevus (M8720/0) - see also Neoplasm, skin, benign
- Newborn (infant) (liveborn)
- Newcastle's conjunctivitis or disease 077.8
- Nezelof's syndrome (pure alymphocytosis) 279.13
- Niacin (amide) deficiency 265.2
- Nicolas-Durand-Favre disease (climatic bubo) 099.1
- Nicolas-Favre disease (climatic bubo) 099.1
- Nicotinic acid (amide) deficiency 265.2
- Niemann-Pick disease (lipid histiocytosis) (splenomegaly) 272.7
- Night
- Nightmare 307.47
- Nipple - see condition
- Nisbet's chancre 099.0
- Nishimoto (-Takeuchi) disease 437.5
- Nitritoid crisis or reaction - see Crisis, nitritoid
- Nitrogen retention, extrarenal 788.9
- Nitrosohemoglobinemia 289.89
- Njovera 104.0
- No
- Nocardiasis - see Nocardiosis
- Nocardiosis 039.9
- Nocturia 788.43