We retrospectively studied the incidence of bacterial cholangitis in 129 infants operated on because of biliary atresia over 5 years. Forty-six of the 101 children who underwent hepatic portoenterostomy had a total of 105 episodes of cholangitis (range one to eight episodes per child). Most episodes occurred within 3 months of the operation. Factors associated with cholangitis included good or partial restoration of bile flow, abnormal intrahepatic bile ducts or cavities at the porta hepatis, and routine postoperative use of antibiotics. External jejunostomy was not effective in preventing cholangitis. In addition to fever and decreased bile flow, increased erythrocyte sedimentation rate and signs of shock were frequently observed. The responsible organisms, most often gram-negative bacteria, were identified in 79 (75%) episodes by blood or liver cultures. Most were susceptible to trimethoprim-sulfamethoxazole and third-generation cephalosporins during the first episode, but only to cephalosporins during later episodes. The incidence of signs of portal hypertension in children with normal serum bilirubin values at age 5 years was not higher in those who had previously experienced one or more episodes of cholangitis.