We performed a histopathological study of two human brains to look at dilated Virchow-Robin (V-R) spaces in the anterior perforated substance and putamen. We measured the diameter of 74 arteries in 54 dilated V-R spaces. In 28 patients without neurological deficits we ascertained the characteristic location of dilated V-R spaces in the anterior perforated substance and basal ganglia on MRI, measuring the distance from 64 foci of cerebrospinal fluid signal intensity to the centre of the mamillary body on 1 mm thick images. In the histopathological study, the mean diameter of the arteries was 39.0 +/- 36.0 microns. Dilatation of the V-R space was observed from the end of the indentation of the pial membrane towards the brain surface along the perforating artery. In the MR images, the mean distance from the dilated V-R space to the mamillary body was 10.0 +/- 4.5 mm. The V-R space was confined to a fixed level in the lower part of the basal ganglia, and not found near the brain surface.