- Universal
- Unknown
- Unna's disease (seborrheic dermatitis) 690.10
- Unresponsiveness, adrenocorticotropin (ACTH) 255.41
- Unsatisfactory
- Unsoundness of mind (see also Psychosis) 298.9
- Unspecified cause of death 799.9
- Unstable
- Untruthfulness, child problem (see also Disturbance, conduct) 312.0
- Unverricht (-Lundborg) disease, syndrome, or epilepsy 345.1
- Unverricht-Wagner syndrome (dermatomyositis) 710.3
- Upper respiratory - see condition
- Upset
- Urachus - see also condition
- Uratic arthritis 274.00
- Urbach's lipoid proteinosis 272.8
- Urbach-Oppenheim disease or syndrome (necrobiosis lipoidica diabeticorum) 250.8 [709.3]
- Urbach-Wiethe disease or syndrome (lipoid proteinosis) 272.8
- Urban yellow fever 060.1
- Urea, blood, high - see Uremia
- Uremia, uremic (absorption) (amaurosis) (amblyopia) (aphasia) (apoplexy) (coma) (delirium) (dementia) (dropsy) (dyspnea) (fever) (intoxication) (mania) (paralysis) (poisoning) (toxemia) (vomiting) 586
- Ureter, ureteral - see condition