- Thrush 112.0
- Thumb - see also condition
- Thygeson's superficial punctate keratitis 370.21
- Thymergasia (see also Psychosis, affective) 296.80
- Thymitis 254.8
- Thymoma (benign) (M8580/0) 212.6
- Thymus, thymic (gland) - see condition
- Thyrocele (see also Goiter) 240.9
- Thyroglossal - see also condition
- Thyroid (body) (gland) - see also condition
- Thyroiditis 245.9
- Thyrolingual duct, persistent 759.2
- Thyromegaly 240.9
- Thyrotoxic
- Thyrotoxicosis 242.9
- TIA (transient ischemic attack) 435.9
- Tibia vara 732.4
- Tic 307.20
- Tick (-borne) fever NEC 066.1
- Tick paralysis 989.5
- Tick-bite fever NEC 066.1
- Tics and spasms, compulsive 307.22
