- At risk for falling V15.88
- Ataxia, ataxy, ataxic 781.3
- Ataxia-telangiectasia 334.8
- Atelectasis (absorption collapse) (complete) (compression) (massive) (partial) (postinfective) (pressure collapse) (pulmonary) (relaxation) 518.0
- Ateleiosis, ateliosis 253.3
- Atelia - see Distortion
- Ateliosis 253.3
- Atelocardia 746.9
- Atelomyelia 742.59
- Athelia 757.6
- Atheroembolism
- Atheroma, atheromatous (see also Arteriosclerosis) 440.9
- Atheromatosis - see also Arteriosclerosis
- Atherosclerosis - see Arteriosclerosis
- Athetosis (acquired) 781.0
- Athlete's
- Athletic team examination V70.3
- Athrepsia 261
- Athyrea (acquired) (see also Hypothyroidism) 244.9
- Athyreosis (congenital) 243
- Athyroidism (acquired) (see also Hypothyroidism) 244.9
- Atmospheric pyrexia 992.0