- Monocytopenia 288.59
- Monocytosis (symptomatic) 288.63
- Monofixation syndrome 378.34
- Monomania (see also Psychosis) 298.9
- Mononeuritis 355.9
- Mononeuropathy (see also Mononeuritis) 355.9
- Mononucleosis, infectious 075
- Monoplegia 344.5
- Monorchism, monorchidism 752.89
- Monteggia's fracture (closed) 813.03
- Mood swings
- Moore's syndrome (see also Epilepsy) 345.5
- Mooren's ulcer (cornea) 370.07
- Mooser bodies 081.0
- Mooser-Neill reaction 081.0
- Moral
- Morax-Axenfeld conjunctivitis 372.03
- Morbilli (see also Measles) 055.9
- Morbus
- Morel-Kraepelin disease (see also Schizophrenia) 295.9
- Morel-Moore syndrome (hyperostosis frontalis interna) 733.3
- Morel-Morgagni syndrome (hyperostosis frontalis interna) 733.3