- Atrioventricularis commune 745.69
- Atrophia - see also Atrophy
- Atrophoderma, atrophodermia 701.9
- Atrophy, atrophic
- Attack
- Attention to
- Attrition
- Atypical - see also condition
- Atypism, cervix 622.10
- Audible tinnitus (see also Tinnitus) 388.30
- Auditory - see condition
- Audry's syndrome (acropachyderma) 757.39
- Aujeszky's disease 078.89
- Aura
- Aurantiasis, cutis 278.3
- Auricle, auricular - see condition
- Auriculotemporal syndrome 350.8
- Australian
- Autism, autistic (child) (infantile) 299.0
- Autodigestion 799.89
- Autoerythrocyte sensitization 287.2
- Autographism 708.3