- Lassitude (see also Weakness) 780.79
- Late - see also condition
- Latent - see condition
- Lateral - see condition
- Laterocession - see Lateroversion
- Lateroflexion - see Lateroversion
- Lateroversion
- Lathyrism 988.2
- Launois' syndrome (pituitary gigantism) 253.0
- Launois-Bensaude's lipomatosis 272.8
- Launois-Cleret syndrome (adiposogenital dystrophy) 253.8
- Laurence-Moon-Biedl syndrome (obesity, polydactyly, and intellectual disabilities) 759.89
- LAV (disease) (illness) (infection) - see Human immunodeficiency virus (disease) (illness) (infection)
- LAV/HTLV-III (disease) (illness) (infection) - see Human immunodeficiency virus (disease) (illness) (infection)
- Lawford's syndrome (encephalocutaneous angiomatosis) 759.6
- Lax, laxity - see also Relaxation
- Laxative habit (see also Abuse, drugs, nondependent) 305.9
- Lazy leukocyte syndrome 288.09
- LCAD (long chain/very long chain acyl CoA dehydrogenase deficiency, VLCAD) 277.85
- LCHAD (long chain 3-hydroxyacyl CoA dehydrogenase deficiency) 277.85
- Lead - see also condition
- Lead miners' lung 503