- Babesia microti
- Babesiosis
- BabyBIG
- Bacillary angiomatosis
- Bacillary peliosis
- Bacillus anthracis
- Bacillus Calmette-Guérin (BCG) vaccine
- Bacillus cereus
- Back pain
- Back to Sleep, 365
- Baclofen withdrawal
- Bacteremia
- Bacterial encephalitis
- Bacterial meningitis
- Bacterial overgrowth
- Bacterial pneumonia
- Bacterial rhinosinusitis
- Bacterial vaginosis
- Bacteroides
- Balanitis
- Balanoposthitis
- Bannayan-Riley-Ruvalcaba syndrome (BRRS)
- Barbiturate coma
- Barbiturate withdrawal
- Bardet-Biedl syndrome
- Bariatric surgery
- Barlow test
- Barotitis
- Barotrauma
- Barrier contraceptives
- Barth syndrome
- Bartonella henselae
- Bart syndrome
- Bartter syndrome
- Basal cell nevus syndrome
- Bath salts
- Bazex-Dupre-Christol syndrome
- B-cell lymphoma
- Beaded hair
- Becker muscular dystrophy
- Beckwith-Wiedemann syndrome
- Bedwetting (nocturnal enuresis)
- Beef tapeworm
- Bee sting
- Behçet syndrome
- Bell-clapper deformity
- Bell palsy
- Benign paroxysmal vertigo of childhood
- Benzodiazepines
- Benzodiazepine withdrawal
- Bethlem muscular dystrophy
- Bezoars
- Bezold abscess
- Bicuspid aortic valve
- Bile acid-binding resins
- Bile acid synthetic defects (BASDs)
- Biliary atresia (BA)
- Biliary atresia splenic malformation (BASM)
- Biliary obstruction
- Biliary tract mass
- Bilirubin
- Bilirubin encephalopathy
- Bilirubin-induced neurologic dysfunction (BIND)
- Binge eating, in bulimia
- Biotinidase deficiency
- Bipolar disorder, depression in
- Birth trauma
- 2,3-Bisphosphoglycerate mutase deficiency
- Bisphosphonates
- Bites
- Bite wounds
- Black measles
- Blackwater fever
- Black widow spider
- Bladder
- Bladder and bowel dysfunction (BBD)
- Bladder exstrophy
- Bladder mass
- Bladder outlet obstruction
- Bladder toxicity, in cancer therapy
- Blalock-Taussig systemic-to-pulmonary artery shunt
- Bland-White-Garland syndrome
- Blastomyces dermatitidis
- Blastomycosis
- Blau syndrome
- Bleach bath, for atopic dermatitis
- Bleeding
- Blepharitis
- Blindness
- Bloch-Sulzberger syndrome
- Blood pressure
- Blood transfusion
- Blood type compatibility
- Bloom syndrome
- Blount disease
- Blue diaper syndrome
- Bochdalek hernia
- Body dysmorphic disorder
- Body lice
- Body mass index (BMI)
- Bone blastomycosis
- Bone marrow failure syndromes
- Bone marrow transplantation
- Bone toxicity, in cancer therapy
- Bordetella parapertussis
- Bordetella pertussis
- Borrelia burgdorferi
- Boston exanthem
- Botulism
- Bourneville disease
- Bovine spongiform encephalopathy
- Bowel dysfunction
- Bowel infarction
- Bowel management
- Bowel necrosis
- Bowel obstruction
- Bowel perforation
- Bowleggedness
- Brachial plexus palsy, perinatal
- Brachmann-De Lange syndrome
- Bracing
- Brain abscess
- Brain death
- Brain herniation
- Brain injury
- Brain lesions, congenital vascular
- Brain tumor
- Branchial cleft cyst
- Branchial cleft malformations
- Branchio-oto-renal syndrome
- Breast abscess
- Breast cellulitis
- Breast development, premature
- Breast engorgement
- Breast enlargement, male
- Breastfeeding
- Breath-holding spells
- Breech birth
- Brief resolved unexplained event (BRUE)
- Brill-Zinsser disease
- Bronchiectasis
- Bronchiolitis
- Bronchiolitis obliterans
- Bronchitis
- Bronchodilators
- Bronchogenic cyst
- Bronchomalacia
- Bronchopulmonary dysplasia (BPD)
- Bronchopulmonary fistula
- Brown recluse spider
- Brown syndrome
- Brucellosis
- Brudzinski sign
- Brugada syndrome
- Bruising
- Bruxism
- Bubble bath urethritis
- Buboes
- Bubonic plague
- Buccal cellulitis
- Buckley syndrome
- Budd-Chiari syndrome
- Bulimia
- Bullous impetigo
- Buried penis
- Burkholderia cepacia
- Burkitt lymphoma
- Burn injuries
- Bursitis
- Butterbur
- Byler disease