Multiple intracranial aneurysms (MIA) have been detected in up to one-third of patients with cerebral aneurysms. Three main external factors influence these figures as follows: the quality of angiographies, the quantity of vessels studied, and referral policy. In a 1-year prospective study, we determined the incidence of MIA in a defined catchment area in East Finland by investigating all of the patients with intracranial aneurysms with panangiography. In 114 unselected patients, a total of 170 intracranial aneurysms were detected, and, of these, 39 (34%) harbored MIA. In contrast to most other reports, there was a male predominance in patients with MIA, and half of these men had hypertension. Intracavernous carotid and pericallosal aneurysms were more frequent in patients with MIA. The number of asymptomatic vertebrobasilar aneurysms was extremely low, and most of the nonruptured aneurysms were found in bilateral carotid angiograms. In spite of the active search, the proportion of vertebrobasilar aneurysms remained at 6%. Although our surgical policy was most active, one-third of the asymptomatic aneurysms remained untreated, mainly because of the poor condition of the patient.