To better understand changes in the size of the extrahepatic bile duct after liver transplantation, we retrospectively studied the luminal diameter of the extrahepatic bile duct on serial cholangiograms in 40 liver transplant recipients with choledochocholedochostomy biliary anastomoses and without biliary complications. Forty operative and 105 postoperative cholangiograms were reviewed. The average interval between operative and last postoperative cholangiogram was 5 weeks (range, 1-17 weeks). The mean diameter of the donor common hepatic duct increased from 5.5 +/- 2.1 mm to 6.3 +/- 2.4 mm (p = .015). The mean diameter of the native common bile duct increased from 5.1 +/- 1.4 mm to 6.8 +/- 2.4 mm (p less than .001). The diameter of the donor common hepatic duct increased by 3 mm or more in six patients (15%); the diameter of the native common bile duct increased by 3 mm or more in nine (23%). Increased diameter of the native common bile duct was associated with T-tube migration into the duct in four cases. The size of the extrahepatic bile duct on cholangiograms is stable or increases slightly in most liver transplant recipients. Mild increases unassociated with a specific cause of obstruction or hepatic dysfunction do not portend biliary obstruction and are clinically benign.