- Bardet-Biedl syndrome
- Batten disease
- Beals syndrome
- Beare-Stevenson cutis gyrata syndrome
- Beckwith-Wiedemann syndrome
- Beta thalassemia
- Bicuspid aortic valve
- Biotinidase deficiency
- Bipolar disorder
- Bloom syndrome
- Blue rubber bleb nevus syndrome
- Brachydactyly
- Branchiootorenal syndrome
- Breast cancer
- Bruton agammaglobulinemia
