- Antithromboplastinogenemia (see also Circulating anticoagulants) 286.59
- Antitoxin complication or reaction - see Complications, vaccination
- Anton (-Babinski) syndrome (hemiasomatognosia) 307.9
- Antritis (chronic) 473.0
- Antrum, antral - see condition
- Anuria 788.5
- Anus, anal - see also condition
- Anusitis 569.49
- Anxiety (neurosis) (reaction) (state) 300.00
- Aorta, aortic - see condition
- Aortectasia (see also Ectasia, aortic) 447.70
- Aortitis (nonsyphilitic) 447.6
- Apathetic 799.25
- Apathy 799.25
- Apepsia 536.8
- Aperistalsis, esophagus 530.0
- Apert's syndrome (acrocephalosyndactyly) 755.55
- Apert-Gallais syndrome (adrenogenital) 255.2
- Apertognathia 524.20
- Aphagia 787.20
- Aphakia (acquired) (bilateral) (postoperative) (unilateral) 379.31
- Aphalangia (congenital) 755.4