Hemorrhage is an uncommon but serious complication of pancreatic pseudocysts. When gastrointestinal bleeding or intra-abdominal hemorrhage is associated with a pancreatic pseudocyst and the usual sources of bleeding are not detected by endos-copy, the rupture of a pseudoaneurysm inside the pseudocyst should be suspected. We present 13 cases, 11 associated with chronic and 2 with late complications after acute necrotizing pancreatitis. On the basis of sonographic findings, bleeding site was suspected in 8 of 11 patients (73%). Computed tomography (CT) was performed on 10, and bleeding was suspected in 8 (80%). The pseudoaneurysm itself was detected by CT in one and by ultrasonography in none. Visceral angiography was performed on five patients, and the pseudoaneurysm was evident in all. External drainage with arterial ligation was done as a primary operation in five patients; four of them later underwent pancreatic resection because of rebleeding. In eight cases pancreatic resection was the initial operation; none of these patients continued to bleed or needed reoperation because of the same pseudoaneurysm. There were no intra-operative deaths, but one patient died postoperatively. Aggressive diagnostic evaluation and surgical approach are associated with a reduction in mortality and morbidity in this serious complication of pancreatic pseudocysts.