See Rare Diseases by First Letter (M)
- Malaria
- Malignant Fibrous Histiocytoma
- Malignant Germ Cell Tumor
- Malignant Hyperthermia
- Malignant Mesenchymal Tumor
- Malignant Mesothelioma
- Malignant Mixed Mullerian Tumor
- Malignant Peripheral Nerve Sheath Tumor
- Malonyl-CoA Decarboxylase Deficiency
- Mansonelliasis
- Mantle Cell Lymphoma
- Maple Syrup Urine Disease
- Marburg Hemorrhagic Fever
- Marfan Syndrome
- Mastocytosis
- Maternal Hyperphenylalaninemia
- Maturity-onset Diabetes of the Young
- McCune Albright Syndrome
- Measles
- Meckel Syndrome
- Meconium Aspiration Syndrome
- Medullary Cystic Kidney Disease
- Medulloblastoma
- Medulloblastoma, Childhood
- Melanoma, Familial
- Meliodosis
- Membranoproliferative Glomerulonephritis Type 2
- Membranous Nephropathy
- Menetrier Disease
- Meningioma
- Meningococcal Infection
- Meningococcemia
- Menkes Disease
- Mercury Poisoning
- Merkel Cell Carcinoma
- Metachromatic Leukodystrophy
- Metastatic Squamous Neck Cancer With Occult Primary
- Methionine Adenosyltransferase Deficiency
- Methylmalonic Acidemia
- Mevalonic Aciduria
- Microcephaly
- Microencephaly
- Microscopic Polyangiitis
- Microsporidiosis
- Midline Lethal Granuloma
- Miller-Fisher Syndrome
- Milroy Disease
- Minimal Change Disease
- Mitochondrial Neurogastrointestinal Encephalopathy Syndrome
- Mitochondrial Trifunctional Protein Deficiency
- Mixed Connective Tissue Disease
- Miyoshi Myopathy
- Moebius Syndrome
- Molybdenum Cofactor Deficiency
- Mondini Dysplasia
- Mondor Disease
- Monkeypox
- Monoclonal Gammopathy of Undetermined Significance
- Montefiore Syndrome
- Morphea
- Morquio Syndrome A
- Morvan's Fibrillary Chorea
- Motor Neuro-ophthalmic Disorders
- Moyamoya Disease
- Muckle-Wells Syndrome
- Mucoepidermoid Carcinoma
- Mucopolysaccharidosis
- Mucopolysaccharidosis Type I
- Mucopolysaccharidosis Type II
- Mucopolysaccharidosis Type III
- Mucopolysaccharidosis Type IIIA
- Mucopolysaccharidosis Type IIIB
- Mucopolysaccharidosis Type VI
- Mucopolysaccharidosis Type VII
- Muenke Syndrome
- Multicentric Castleman’s Disease
- Multicore Disease
- Multifocal Choroiditis
- Multifocal Lymphangioendotheliomatosis With Thrombocytopenia
- Multiple Endocrine Neoplasia Type 1
- Multiple Endocrine Neoplasia Type 2
- Multiple Endocrine Neoplasia Type 2A
- Multiple Endocrine Neoplasia Type 2B
- Multiple Myeloma
- Multiple System Atrophy
- Multiple System Atrophy (MSA) With Orthostatic Hypotension
- Mumps
- Muscle Eye Brain Disease
- Muscular Dystrophy
- Myasthenia Gravis
- Mycobacterium Abscessus
- Mycobacterium Avium Complex
- Mycobacterium Xenopi
- Mycoplasmal Pneumonia
- Mycosis Fungoides
- Myelitis
- Myelodysplastic Syndromes
- Myelodysplastic/myeloproliferative Disease
- Myelofibrosis
- Myelomeningocele
- MYH9 Related Thrombocytopenia
- Myocarditis
- Myoclonus Epilepsy
- Myopathy Congenital
- Myotonia Atrophica
- Myotonic Dystrophy
- Myotonic Dystrophy Type 1
- Myotubular Myopathy
- Myxoid Liposarcoma
- Myxopapillary Ependymoma