The association of intracranial aneurysm with ADPKD is well-known, and patients with ADPKD are at increased risk of subarachnoid hemorrhage from rupture of intracranial aneurysms. We prospectively performed three-dimensional time-of-flight magnetic resonance angiography (MRA) in 30 nonselective adult patients with ADPKD. Sixteen were women and 14 were men with a mean age of 51 yr (range 24 to 79 yr). The diagnosis of ADPKD was made on the basis of abdominal ultrasound or computed tomographic studies. Three patients were on maintenance hemodialysis, 8 patients were nondialysed patients with chronic renal failure (serum creatinine > or = mg/dl) and 25 patients had hypertension (BP > or = 140/90 mmHg). None of these patients have a previous diagnosis of intracranial aneurysm. Unruptured intracranial aneurysms were suspected in 5 patients by MRA, and 8 aneurysms were confirmed in 4 (13.3%) of 30 patients by conventional arteriography. These aneurysms were 3 approximately 10 mm in diameter and 3 aneurysms (3 approximately 4 mm in diameter) were newly detected by cerebral arteriography. After informed consent was obtained, neck clipping of the intracranial aneurysms were performed successfully in all the patients. These results suggest that the prevalence of intracranial aneurysms is about 13% in ADPKD, and that MRA is useful in screening for occult intracranial aneurysms in patients with ADPKD.