- Autoradiography
- Autosome
- AV node
- Avascular necrosis
- Avulsion
- Axilla
- Axillary dissection
- Azotemia
- B cell
- Baby, fetal alcohol syndrome
- Back pain, low
- Bacterium
- Bacteriophage
- Bag of waters
- Baker cyst
- Baldness
- Balloon angioplasty
- Banding of chromosomes
- Barium enema
- Barium solution
- Barium swallow
- Barlow syndrome
- Barosinusitis
- Barotitis
- Barotrauma, otic
- Barotrauma, sinus
- Barr body
- Barrett esophagus
- Basal cells
- Basal cell carcinoma
- Basal metabolic rate
- Base in DNA
- Base pair
- Base sequence
- Base sequence analysis
- Battle fatigue
- Bee sting
- Beef tapeworm
- Behcet's syndrome
- Belching