Preduodenal portal vein (PDPV) is a rare developmental anomaly in which the portal vein runs at the ventral side of the duodenum instead of at an intrapancreatic location. Understanding of this anomaly is of considerable surgical importance, because it may cause unintended portal vein injury during operations involving the gall bladder or duodenum. We recently experienced PDPV associated with polysplenia syndrome in a 49-year-old male patient who complained of persistent epigastric pain. CT portal venography with thin slab maximal intensity projection and volume rendering demonstrated the unique feature of convex anastomosis between the L-shaped mesenterico-portal vein and mesenterico-splenic vein in the mid abdomen. We report here the Multidetector-row CT findings of a rare case of PDPV.