- Babesiosis
- Bacterial arthritis
- Bacterial endocarditis
- Bacterial meningitis
- Bacterial pneumonia
- Bacterial vaginosis
- Barrett's esophagus
- Basal cell carcinoma of skin
- Becker muscular dystrophy
- Beckwith-Wiedemann syndrome
- Behçet’s disease
- Benign endometrial hyperplasia
- Benign essential hypertension
- Benign islet cell tumor
- Benign neoplasm of bronchus and lung
- Benign neoplasm of esophagus
- Benign neoplasm of liver and/or biliary ducts
- Benign neoplasm of peripheral nerve
- Benign neoplasm of rectum and anal canal
- Benign neoplasm of thymus
- Benign neoplasm, adrenal gland
- Benign neoplasm, bladder
- Benign neoplasm, brain
- Benign neoplasm, colon
- Benign neoplasm, kidney
- Benign neoplasm, ovary
- Benign neoplasm, pancreas
- Benign neoplasm, pituitary gland (pituitary adenoma)
- Benign neoplasm, prostate
- Benign neoplasm, spinal cord
- Benign neoplasm, stomach
- Benign neoplasm, testis
- Benign neoplasm, thyroid gland
- Benign neoplasm, uterine cervix
- Benign prostatic hypertrophy
- Beta-Thalassemia
- Biotinidase deficiency
- Bipolar disorder
- Blastomycosis
- Bloom syndrome
- Bohring-Opitz syndrome
- Bone Tumors and Bone Sarcomas
- Breast cancer screening
- Breast tumor
- Bronchiectasis
- Bronchopneumonia
- Bronchopulmonary dysplasia of newborn
- Brucellosis
- Brugada syndrome
- Budd-Chiari syndrome
- Bullous pemphigoid
- Burkitt lymphoma
- Burns
- Major depressive disorder (Depression)
- Malabsorption
- Malaria
- Male infertility
- Malignant Neoplasm, Fallopian tube
- Malignant Neoplasms, Bone and articular cartilage (Osteosarcoma)
- Malignant hyperthermia
- Malignant neoplasm of Retina
- Malignant neoplasm of anus and anal canal
- Malignant neoplasm of esophagus
- Malignant neoplasm of head and neck
- Malignant neoplasm of lung
- Malignant neoplasm of oropharynx
- Malignant neoplasm of pharynx
- Malignant neoplasm of thymus
- Malignant neoplasm, adrenal gland
- Malignant neoplasm, brain
- Malignant neoplasm, cervix
- Malignant neoplasm, colon
- Malignant neoplasm, endocervix
- Malignant neoplasm, endometrium
- Malignant neoplasm, extrahepatic bile duct
- Malignant neoplasm, female breast
- Malignant neoplasm, gallbladder
- Malignant neoplasm, intrahepatic bile duct
- Malignant neoplasm, liver
- Malignant neoplasm, male breast
- Malignant neoplasm, ovary
- Malignant neoplasm, pancreas
- Malignant neoplasm, pituitary gland
- Malignant neoplasm, prostate
- Malignant neoplasm, renal pelvis
- Malignant neoplasm, spinal cord
- Malignant neoplasm, stomach
- Malignant neoplasm, thyroid gland
- Malignant neoplasm, ureter
- Malignant neoplasm, urinary bladder
- Malignant neoplasm, uterine cervix (cervical cancer)
- Malignant tumor of thyroid gland
- Mantle cell lymphoma
- Maple syrup urine disease
- Marfan Syndrome
- Mastitis
- Measles (rubeola)
- Medullary thyroid carcinoma
- Megaloblastic anemia
- Melanocytic nevus
- Melanoma
- Membranoproliferative glomerulonephritis
- Meningioma
- Meningitis due to gram negative bacteria
- Menopause
- Metabolic acidosis
- Metabolic alkalosis
- Metabolic syndrome
- Metachromatic leukodystrophy
- Metastatic colon cancer
- Methanol poisoning
- Methemoglobinemia
- Methicillin resistant Staphylococcus aureus infection
- Migraine
- Miliary tuberculosis
- Miller-Dieker Syndrome
- Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes (MELAS)
- Mixed acid-base balance disorder
- Mixed connective tissue disease
- Monoclonal Gammopathy of Undetermined Significance (MGUS)
- Mucolipidosis type IV
- Mucopolysaccharidosis VI (Maroteaux-Lamy syndrome)
- Mucopolysaccharidosis type I
- Mucopolysaccharidosis type IH
- Mucopolysaccharidosis type II (Hunter Syndrome)
- Mucopolysaccharidosis type III
- Multifactorial encephalopathy
- Multinodular goiter
- Multiple endocrine neoplasia, type I
- Multiple endocrine neoplasia, type II
- Multiple endocrine neoplasia, type III
- Multiple myeloma
- Multiple sclerosis
- Multiple sulfatase deficiency
- Mumps
- Muscular dystrophy
- Myasthenia gravis
- Mycoplasma and Ureaplasma Genito-urinary Infections
- Mycoplasma pneumonia
- Mycosis
- Myelodysplastic syndrome
- Myocarditis
- Myotonic dystrophy