This retrospective cohort study aimed at determining whether overweight children undergoing allogeneic stem cell transplantation (SCT) had inferior overall survival compared with children who were not overweight. Children >/=2 years of age who received allogeneic SCT were included. Overweight was defined as a body mass index >/= 95th percentile; 54/325 (17%) children were overweight. Overall survival at 5 years was significantly inferior at 46.6 +/- 7.3% in the overweight group compared with 59.5 +/- 3.2% in the non-overweight group (P = 0.02). Our study demonstrated that overweight children who undergo allogeneic SCT had inferior survival compared with children who were not overweight.