Reconstruction of the hepatic vein (HV) is not required in size-matched orthotopic liver transplantation (OLT) because the vena cava (VC) is replaced. In reduced size OLT, used for providing small livers for children, the HV is often implanted directly. Grafts obtained from a split liver in which the right lobe is used for a second recipient or from a live donor must be implanted without the VC. To evaluate the occurrence of outflow complications and their prevention, we have reviewed our experience with 72 left sided reduced grafts in children. Between July 1985 and November 1990, 93 reduced grafts were performed. Twenty-one were right lobe grafts with orthotopic replacement of the VC. Seventy-two were left grafts comprising 28 full left lobes and 44 lateral segments. Grafts were obtained from reduction of a cadaver liver in 39, from the left lobe of a split liver in 21 and from a live donor in 12. Of the left grafts, 47 were implanted with preservation of the recipient VC. Overall, HV obstruction occurred in 12 patients. Obstruction occurred acutely in three patients, causing graft failure and death in two and was repaired successfully in one patient. Chronic HV obstruction was documented in three patients with ascites and graft enlargement requiring retransplantation. This complication occurred in five of 25 patients with VC, six of 18 with end to end HV anastomosis, one of 18 with end to side implantation of HV and zero of 15 using a triangular anastomosis (p = 0.05). Outflow obstruction has not received adequate attention in descriptions of reduced-size OLT. Marked hepatic swelling and fluid retention that occur after reduced size hepatic transplantation may be the result of incomplete HV obstruction. In this series, end to end anastomosis of the HV resulted in a high frequency of outflow obstruction. This was prevented when anastomoses were designed to allow the graft to rest comfortably in the hepatic fossa after abdominal closure.