A 55-year-old man was admitted to our hospital to evaluate a large pseudocyst. Computed tomography showed a 5-cm pseudocyst filled with contrast medium in the head of the pancreas, and color Doppler ultrasonography revealed high-velocity pulsatile flow inside the cyst. Celiac angiography confirmed bleeding from the superior anterior pancreaticoduodenal artery into the cyst. Pancreaticoduodenectomy was performed. Pathologic examination showed a thick-walled pseudocyst filled with clots. The postoperative course was uneventful. Five years after the operation, the patient remained free from bleeding. Bleeding from pancreatic pseudoaneurysms may cause sudden death in patients with chronic pancreatitis, therefore, this entity should be borne in mind, and prompt treatment is of utmost importance in cases of major bleeding.