- Bloch-Siemens syndrome (incontinentia pigmenti) 757.33
- Bloch-Stauffer dyshormonal dermatosis 757.33
- Bloch-Sulzberger disease or syndrome (incontinentia pigmenti) (melanoblastosis) 757.33
- Block
- Blocq's disease or syndrome (astasia-abasia) 307.9
- Blood
- Blood-forming organ disease 289.9
- Bloodgood's disease 610.1
- Bloodshot eye 379.93
- Bloom (-Machacek) (-Torre) syndrome 757.39
- Blotch, palpebral 372.55
- Blount's disease (tibia vara) 732.4
- Blount-Barber syndrome (tibia vara) 732.4
- Blue
- Blueness (see also Cyanosis) 782.5
- Blurring, visual 368.8
- Blushing (abnormal) (excessive) 782.62
- BMI (body mass index)
- Boarder, hospital V65.0
- Bockhart's impetigo (superficial folliculitis) 704.8
- Bodechtel-Guttmann disease (subacute sclerosing panencephalitis) 046.2
- Boder-Sedgwick syndrome (ataxia-telangiectasia) 334.8
