- Macroglossia
- Macular Degeneration
- Magnesium Deficiency
- Malaria
- Mandibulofacial Dysostosis
- Mannosidosis
- Maple Syrup Urine Disease
- Marfan Syndrome
- Mastocytosis
- Measles
- Meckel’s Diverticulum
- Mediterranean Fever, Familia
- Meige Syndrome
- Melanoma
- Melas Syndrome
- Memory Disorders
- Meniere’s Disease
- Meningioma
- Meningitis, Bacterial
- Meningitis, Viral
- Menke’s Syndrome
- Myotubular Myopathy
- Melioidosis
- Menstruation Disorders
- Mental Retardation
- Mercury Poisoning
- Mesothelioma
- Microcephaly
- Migraine
- Mite Infestations
- Mitochondrial Diseases
- Mitochondrial Myopathies
- Mitral Valve Prolapse
- Mixed Connective Tissue Disease
- Moebius Syndrome
- Motion Sickness
- Motor Neuron Disease
- Mouth Neoplasms
- Moyamoya Disease
- Mucocutaneous Lymph Node Syndrome
- Mucopolysaccharidoses
- Multiple Myeloma
- Mumps
- Multiple Sclerosis
- Muscle Cramp
- Muscular Atrophy, Spinal
- Muscular Dystrophy
- Muscular Spasticity
- Musculoskeletal Abnormalities
- Mutism
- Myasthenia Gravis
- Mycobacterium Infections
- Mycoplasma Infection
- Myelitis
- Myelodysplastic Syndrome
- Myeloproliferative Disorders
- Myiasis
- Myocardial Infarction
- Myocardial Ischemia
- Myocarditis
- Myoclonus
- Myopathies, Congenital
- Myopia
- Myositis