- Aorta, aortic - see condition
- Aortectasia 441.9
- Aortitis (nonsyphilitic) 447.6
- Apathetic thyroid storm (see also Thyrotoxicosis) 242.9
- 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
- Aphasia (amnestic) (ataxic) (auditory) (Broca's) (choreatic) (classic) (expressive) (global) (ideational) (ideokinetic) (ideomotor) (jargon) (motor) (nominal) (receptive) (semantic) (sensory) (syntactic) (verbal) (visual) (Wernicke's) 784.3
- Aphemia 784.3
- Aphonia 784.41
- Aphthae, aphthous - see also condition
- Apical - see condition
- Apical ballooning syndrome 429.83
- Aplasia - see also Agenesis
- Apleuria 756.3
- Apnea, apneic (spells) 786.03
- Apneumatosis newborn 770.4