The left lateral segment of the liver from an adult living donor sometimes is relatively too large for a small pediatric recipient. It currently is unknown whether a high graft-recipient body weight ratio (GRWR) has a significant effect on core temperature during the anhepatic and reperfusion phases of living donor liver transplantation (LDLT). Seventy-two pediatric patients undergoing LDLT were divided into two groups according to body weight. Group I (GI) consisted of patients with a body weight greater than 10 kg, and group II (GII), less than 10 kg. Core temperature, measured as nasopharyngeal temperature (NT), was compared between groups at induction of anesthesia, hourly during the following 6 hours, as the lowest core temperature at the anhepatic phase, 5 and 30 minutes after reperfusion, and the last 2 hours before the end of the operation. Mild hypothermia of 35.8 degrees C +/- 0.7 degrees C and 35.9 degrees C +/- 0.4 degrees C for GI and GII was noted after induction of anesthesia, respectively; this increased +/- 1 degrees C in the following 6 hours. In the anhepatic and reperfusion phases, a sudden and significant decrease in NT was observed in both groups. This decrease in NT was significantly greater in GII than GI. In conclusion, a sudden decrease in core temperature was observed during the anhepatic and reperfusion phases of LDLT in pediatric patients, likely caused by placement of the cold liver graft, which is flushed with 4 degrees C lactated Ringer's solution during vessel reconstruction, in the anhepatic phase and return of venous blood through the cold preserved liver in the reperfusion phase. Core temperatures of pediatric patients with a body weight less than 10 kg in GII, who received grafts with a high GRWR, were more affected than those in GI.