True pancreaticoduodenal artery (PDA) aneurysms are extremely rare. We report herein a case of a ruptured PDA aneurysm associated with a nonruptured splenic artery aneurysm which was successfully treated by surgery. A 55-year-old man was admitted to a local hospital complaining of sudden abdominal and back pain, and thereafter he was transferred to our university hospital. Abdominal computed tomography revealed retroperitoneal hematoma and an enhanced round spot suggesting a peripancreatic aneurysm. Emergency angiography showed a 20-mm-sized aneurysm in the inferior PDA and a 10-mm-sized aneurysm in the splenic artery. The patient underwent an emergency laparotomy with a diagnosis of a ruptured PDA aneurysm. After evacuating a large volume clot in the right retroperitoneal space and the peritoneal cavity, we detected an index finger-sized aneurysm with arterial bleeding in the right inferioposterior aspect of the pancreas. Hemostasis was obtained by oversewing the aneurysm and a ligation of the feeding arteries. A prophylactic splenectomy was performed for the nonruptured splenic artery aneurysm. This case indicates that emergency angiography is indispensable for both a definitive diagnosis and adequate surgical treatment of PDA aneurysms.