Splenic artery aneurysms are an uncommon form of vascular disease that have a significant potential for rupture, resulting in life-threatening intraperitoneal hemorrhage. We describe the case of a 33-year-old man who died suddenly and unexpectedly due to the rupture of a splenic artery aneurysm. At medicolegal autopsy, 3000 mL of fluid blood were recovered from the peritoneal cavity. The source of bleeding was a sack-like aneurysm of the splenic artery, measuring 2 cm in diameter. Histologic examination of the splenic artery aneurysm revealed fibromuscular dysplasia. No atherosclerotic lesions or any inflammatory changes were apparent within the wall of the splenic artery. Portal hypertension and pancreatitis, previously described as important factors promoting splenic artery aneurysm formation, were excluded by autopsy and histology. From the forensic pathologist's viewpoint, this rare case underlines the importance of splenic artery aneurysm rupture as a relevant differential diagnosis of intraperitoneal hemorrhage and sudden death, respectively, since such cases may be misinterpreted as a result of blunt-force trauma.