- Irritable - see Irritability
- Irritation
- Isambert's disease 012.3
- Ischemia, ischemic 459.9
- Ischialgia (see also Sciatica) 724.3
- Ischiopagus 759.4
- Ischium, ischial - see condition
- Ischomenia 626.8
- Ischuria 788.5
- Iselin's disease or osteochondrosis 732.5
- Islands of
- Islet cell tumor, pancreas (M8150/0) 211.7
- Isoimmunization NEC (see also Incompatibility) 656.2
- Isolation V07.0
- Isosporosis 007.2
- Issue
- Itch (see also Pruritus) 698.9
- Itsenko-Cushing syndrome (pituitary basophilism) 255.0
- Ivemark's syndrome (asplenia with congenital heart disease) 759.0
- Ivory bones 756.52
- Ixodes 134.8
- Ixodiasis 134.8
