- Approximal wear 521.10
- Apraxia (classic) (ideational) (ideokinetic) (ideomotor) (motor) 784.69
- Aptyalism 527.7
- Aqueous misdirection 365.83
- Arabicum elephantiasis (see also Infestation, filarial) 125.9
- Arachnidism 989.5
- Arachnitis - see Meningitis
- Arachnodactyly 759.82
- Arachnoidism 989.5
- Arachnoiditis (acute) (adhesive) (basic) (brain) (cerebrospinal) (chiasmal) (chronic) (spinal) (see also Meningitis) 322.9
- Araneism 989.5
- Arboencephalitis, Australian 062.4
- Arbor virus, arbovirus (infection) NEC 066.9
- Arborization block (heart) 426.6
- ARC 042
- Arc-welders' lung 503
- Arc-welders' syndrome (photokeratitis) 370.24
- Arcadiacus amorphus 759.89
- Arches - see condition
- Arcuate uterus 752.36
- Arcuatus uterus 752.36
- Arcus (cornea)