Polyarteritis nodosa (PAN) is a rare systemic necrotizing arteritis that involves small- and medium-sized arteries in various organs. Although aneurysm formation in visceral arteries is a typical finding in PAN, intracranial aneurysms are much less common, and only a few cases of aneurysm rupture associated with this disease have been documented. In this paper, the authors report on a ruptured PAN aneurysm of the anterior cerebral artery; the lesion was trapped and resected. On histological examination, extensive fibrinoid necrosis and an inflammatory infiltration of leukocytes were seen in the aneurysm wall. To the authors' knowledge this is the first report of subarachnoid hemorrhage from a histologically confirmed PAN aneurysm.