The surgical anatomy of six patients with sinistroposition of the gallbladder is described. Five of these were encountered in a consecutive series of 1764 patients undergoing laparoscopic cholecystectomy for symptomatic gallstone disease in two hospitals between 1989 and 1994, a prevalence of 0·3 per cent in patients undergoing this operation. Despite the left-sided transposition of the gallbladder, the biliary pain experienced by these patients was always on the right side. Preoperative diagnosis of this anomaly was made in only one of six patients despite routine preoperative external ultrasonography and selective preoperative cholangiography. In sinistroposition the cystic artery always crosses in front of the common bile duct from right to left. The cystic duct may open on the left or right side of the common hepatic duct. The anomaly does not preclude safe laparoscopic cholecystectomy but modifications of the port sites and use of the falciform lift facilitate the procedure in these cases. The anatomical features of the sixth case encountered in a patient undergoing resection of hilar cholangiocarcinoma indicate that sinistroposition of the gallbladder may be due to failure of development of segment IV of the liver.