Hepatic hemodynamic changes during liver transplantation (OLT) in children have not yet been studied. We measured intraoperative portal vein flow (PVF) and hepatic arterial flow (HAF) (mL/min) in 53 children and 58 grafts during OLT. Flows were measured in the native organ and in the allograft. In the native liver, PVF and HAF are similar; after transplantation they return to the physiological situation. No flow differences were seen between whole and partial grafts. Among the 8 (14%) portal vein thromboses, PVF was lower in both the native liver and the graft than in the no thrombosis group (P < .05). PVF <5 mL/min/kg was a risk factor to develop PV thrombosis. No graft loss occurred in 3 cases without PVF at the time of OLTs despite the observation that repermeabilization was not possible. In 4 patients with PVF <5 mL/min/kg, after tying a spontaneous spleno-renal shunt (n = 3) or performing a porto-renal vein anastomosis (n = 1), PVF reached >20 mL/min/kg, avoiding thrombosis. In conclusion, PVF and HAF measurements during pediatric OLT may predict patients at high risk for development of PV thrombosis.