The 65 reports of accidental lesions of the choledochus at cholecystectomy from the records of the Patients' Insurance Syndicate in Stockholm, Sweden, 1975-1982, were studied in order to characterize avoidable factors and/or situations at cholecystectomy. Compared with control materials, there were significantly less men (28 vs. 34%) and the patients were younger (46 vs. 54 years). The patients were without significant other diseases and former operations, and were slim or of a normal weight. The patients had a short history of known biliary tract disease and there was seldom a suspicion of common duct stone. Most of the surgeons were under training and 80% of them had done 25 to 100 cholecystectomies before, seldom assisted by a more experienced surgeon. The inflammation was never severe, the bleeding insignificant, and an anomaly was found after the lesion was done in only 16 of 55 cases. The lesion was done before cholangiography in 27 cases and after the cholangiography, but before the films were available in 32 cases. The gallbladder was excised about as often from the fundus as from the pouch. We have found it probable that most of these accidental injuries of the choledochus could have been prevented with a policy that considers cholecystectomy as a major operation that requires well-trained surgeons with a humble and concentrated approach to their task.