The angiographic features of three cases with holoprosencephaly are reported. In all of them, the galenic venous system seemed to be deficient and the basal ganglia were drained by peculiar veins which coursed laterally and drained directly into the lateral sinus. These peculiar veins are considered to be remnants of the embryonic diencephalic veins, suggesting that these patients retain their early embryonic pattern of venous drainage. The diagnosis of alobar holoprosencephaly is established by the demonstration of the azygos anterior cerebral artery coursing along the frontal bone with excessive undulations. But with lobar holoprosencephaly, this characteristic feature is not present, and dysgenesis of the deep venous system is important for the diagnosis of holoprosencephaly.