- Undernutrition 269.9
- Underweight 783.22
- Underwood's disease (sclerema neonatorum) 778.1
- Undescended - see also Malposition, congenital
- Undetermined diagnosis or cause 799.9
- Undeveloped, undevelopment - see also Hypoplasia
- Undiagnosed (disease) 799.9
- Undulant fever (see also Brucellosis) 023.9
- Unemployment, anxiety concerning V62.0
- Unequal leg (acquired) (length) 736.81
- Unerupted teeth, tooth 520.6
- Unextracted dental root 525.3
- Unguis incarnatus 703.0
- Unicornis uterus 752.33
- Unicornuate uterus (with or without a separate uterine horn) 752.33
- Unicorporeus uterus 752.39
- Uniformis uterus 752.39
- Unilateral - see also condition
- Unilateralis uterus 752.39
- Unilocular heart 745.8
- Uninhibited bladder 596.54
- Union, abnormal - see also Fusion