- AAT (alpha-1 antitrypsin) deficiency 273.4
- AAV (disease) (illness) (infection) - see Human immunodeficiency virus (disease) (illness) (infection)
- Abactio - see Abortion, induced
- Abactus venter - see Abortion, induced
- Abarognosis 781.99
- Abasia (-astasia) 307.9
- Abderhalden-Kaufmann-Lignac syndrome (cystinosis) 270.0
- Abdomen, abdominal - see also condition
- Abdominalgia 789.0
- Abduction contracture, hip or other joint - see Contraction, joint
- Abercrombie's syndrome (amyloid degeneration) 277.39
- Aberrant (congenital) - see also Malposition, congenital
- Aberratio
- Aberration - see also Anomaly
- Abetalipoproteinemia 272.5
- Abionarce 780.79
- Abiotrophy 799.89
- Ablatio
- Ablation
- Ablepharia, ablepharon, ablephary 743.62
- Ablepsia - see Blindness
- Ablepsy - see Blindness