From August, 1981, to August, 1982, the authors performed four-vessel angiography in 17 patients with polycystic kidney disease (PKD) who had no neurological deficit and no history of subarachnoid hemorrhage. Seven cases of unruptured aneurysms were found among these 17 patients (an incidence of 41.2%). Five of the unruptured aneurysms were operated on prophylactically, with no mortality or morbidity. Nine of the 17 patients had hypertension and, of these, two (22.2%) had aneurysms. Of the eight patients without hypertension, five (62.5%) had aneurysms. This study suggests that the coexistence of PKD and intracranial aneurysms might not be due to the hypertension that occurs concomitant with PKD, but instead may be attributable to congenital factors. The authors stress the necessity of early diagnosis and early operation for unruptured aneurysms in patients with PKD.