Diagnosaurus
- MAC
- Macrocytic anemia
- Macroglossia
- Macular degeneration, age-related
- Magnesium, decreased serum
- Magnesium, increased serum
- MAHA
- Malabsorption
- Malaria
- Malar rash
- Male hypogonadism
- Malignant ascites
- Malignant melanoma
- Malingering
- Mallory-Weiss syndrome
- Malnutrition
- Mania
- Manic depression
- Marfan syndrome
- Mastalgia
- Mastitis
- MAT
- Measles (rubeola)
- Mediastinal mass
- Megacolon
- Melanoma, malignant
- Melena
- Membranous nephropathy
- Memory loss
- Ménière's disease
- Meningitis
- Meningitis, carcinomatous
- Meniscus tear
- Menopause
- Menorrhagia
- Menstrual bleeding, heavy
- Menstruation, painful
- MEN syndromes
- Mental status, altered
- Mesenteric ischemia, acute
- Mesenteric ischemia, chronic
- Mesothelioma
- Metabolic acidosis, increased anion gap
- Metabolic acidosis, normal anion gap
- Metabolic alkalosis
- Metastases to bone
- Metastases to brain
- Metastases to heart
- Metastases to kidney
- Metastases to liver
- Metastases to lung
- Metastases to meninges
- Metastases to skin
- Metastases to spinal cord
- Methanol poisoning
- Methemoglobinemia
- MGUS
- Microalbuminuria
- Microangiopathic hemolytic anemia
- Microcytic anemia
- Microscopic polyangiitis
- Microsporidiosis
- Migraine
- Migratory arthritis
- Miliaria (heat rash)
- Mitral regurgitation
- Mitral stenosis
- Mixed connective tissue disease
- Molluscum contagiosum
- Monoclonal gammopathy of uncertain significance
- Morbilliform rash
- Motility disorders, esophageal
- Mountain sickness
- Mouth, dry
- Movement disorders
- Multifocal atrial tachycardia
- Multiple endocrine neoplasia
- Multiple myeloma
- Multiple sclerosis
- Mumps
- Munchausen syndrome
- Murmur, diastolic
- Murmur, systolic
- Muscle cramps
- Muscle pain
- Myalgia
- Myasthenia gravis
- Mycobacterium avium complex
- Mycosis fungoides
- Myelodysplastic syndromes
- Myelofibrosis
- Myeloma, multiple
- Myocardial infarction, acute
- Myocarditis, acute
- Myoclonus
- Myopathy
- Myositis
- Myxedema
- Myxoma, atrial