['The pathogenesis and diagnostic methods for idiopathic normal pressure hydrocephalus (iNPH) have been active areas of research in recent years. This study was performed to determine whether there is a venous return abnormality in the intracranial circulation of patients with iNPH.', 'The subjects were 20 patients with iNPH (Group N) and 24 normal controls (Group C). MR venography (MRV) was performed at the superior sagittal sinus 2 cm above the confluence of the sinuses, and the flow velocities were compared between Groups N and C.', 'During normal breathing, the maximum velocities were significantly lower in Group N (18.8 cm/second) than in Group C (22.9 cm/second; (P < .01). During the Valsalva maneuver, compared to normal breathing, the velocity decreased in both groups, but both the maximum (Max V) and minimum (Min V) velocities were significantly lower in Group N than in Group C (P < .01).'] Is flow velocity of the superior sagittal sinus reduced in patients with idiopathic normal pressure hydrocephalus?