The correlation between an aberrant pancreaticoduodenal vein and a portal perfusion defect in the dorsal part of segment IV as demonstrated on CT arterial portography (CTAP) was investigated. 14 patients with non-tumorous defects of portal perfusion in the dorsal part of segment IV of the liver parenchyma, shown on CTAP underwent CT during pancreaticoduodenal arteriography. The defect on CTAP was shown as an enhanced area resulting from non-portal venous inflow in eight (57%) of 14 patients on CT during pancreaticoduodenal arteriography. In conclusion, the non-portal venous supply via an aberrant pancreaticoduodenal vein occasionally causes a defect of portal perfusion in the dorsal part of segment IV on CT arterial portography.