- Arizona enteritis 008.1
- Arm - see condition
- Armenian disease 277.31
- Arnold-Chiari obstruction or syndrome (see also Spina bifida) 741.0
- Arousals
- Arrest, arrested
- Arrhenoblastoma (M8630/1)
- Arrhinencephaly 742.2
- Arrhythmia (auricle) (cardiac) (cordis) (gallop rhythm) (juvenile) (nodal) (reflex) (sinus) (supraventricular) (transitory) (ventricle) 427.9
- Arrillaga-Ayerza syndrome (pulmonary artery sclerosis with pulmonary hypertension) 416.0
- Arsenical
- Arsenism 985.1
- Arterial - see condition
- Arteriectasis 447.8
- Arteriofibrosis - see Arteriosclerosis
- Arteriolar sclerosis - see Arteriosclerosis
- Arteriolith - see Arteriosclerosis
- Arteriolitis 447.6
- Arteriolosclerosis - see Arteriosclerosis
- Arterionephrosclerosis (see also Hypertension, kidney) 403.90
- Arteriopathy 447.9
- Arteriosclerosis, arteriosclerotic (artery) (deformans) (diffuse) (disease) (endarteritis) (general) (obliterans) (obliterative) (occlusive) (senile) (with calcification) 440.9