- Merycism - see also Vomiting
- Merzbacher-Pelizaeus disease 330.0
- Mesaortitis - see Aortitis
- Mesarteritis - see Arteritis
- Mesencephalitis (see also Encephalitis) 323.9
- Mesenchymoma (M8990/1) - see also Neoplasm, connective tissue, uncertain behavior
- Mesenteritis
- Mesentery, mesenteric - see condition
- Mesio-occlusion 524.23
- Mesiodens, mesiodentes 520.1
- Mesocardia (with asplenia) 746.87
- Mesocolon - see condition
- Mesonephroma (malignant) (M9110/3) - see also Neoplasm, by site, malignant
- Mesophlebitis - see Phlebitis
- Mesostromal dysgenesis 743.51
- Mesothelioma (malignant) (M9050/3) - see also Neoplasm, by site, malignant
- Metabolic syndrome 277.7
- Metabolism disorder 277.9
- Metagonimiasis 121.5
- Metagonimus infestation (small intestine) 121.5
- Metal
- Metalliferous miners' lung 503