Hemorrhage is the most frequent complication of endoscopic sphincterotomy, with a reported incidence of 2 to 9 per cent. Previous reports have generally defined this complication clinically, leaving the issue of occult bleeding after sphincterotomy essentially unaddressed. Seventy-five serial sphincterotomies were reviewed to further assess this complication. Nine patients had clinically evident hemorrhage and 27 patients had occult bleeding manifested only by a decrement in hematologic parameters, for a total postsphincterotomy bleeding rate of 48 per cent. No statistically significant risk factors for bleeding were delineated. Endoscopically recognized bleeding at the time of the sphincterotomy was 47 per cent sensitive and 85 per cent specific in predicting postprocedural bleeding. Significant delayed hemorrhage was manifest in three patients, one of whom had clinically occult bleeding. We conclude that bleeding complicates endoscopic sphincterotomy much more frequently than previously reported, although often in a clinically occult manner. Significant delayed bleeding can occur, and may not be clinically apparent. Bleeding recognized endoscopically at the time of sphincterotomy is an insensitive but relatively specific predictor of postprocedural bleeding. As use of endoscopic sphincterotomy increases, careful surveillance for hemorrhagic complications, as well as efforts to identify factors predisposing to the same, will be of increasing importance.