Recurrent acute myeloid leukemia (AML) after hematopoietic stem cell transplantation (HSCT) predicts a dismal prognosis. We sought to determine whether a second HSCT would result in long-term disease-free survival with acceptable toxicity. We evaluated the outcome of a second HSCT with a preparative regimen of cyclophosphamide and total body irradiation in pediatric patients with AML who relapsed after an initial HSCT with a busulfan and cyclophosphamide preparative regimen. Twenty-five patients aged 1.1 to 17.2 years (median, 4.1 years) with AML received a second HSCT for recurrent disease. All patients were conditioned with busulfan and cyclophosphamide for the first HSCT and with cyclophosphamide and total body irradiation for the second HSCT. Donor sources for the first HSCT were autologous (n = 11) or allogeneic (n = 14), whereas all donors for the second HSCT were allogeneic (12 matched related, 9 mismatched related, and 4 unrelated). Engraftment after the second HSCT occurred in all patients at median of 19.0 days (range, 11-32 days). The cumulative incidence of grade II to IV graft-versus-host disease was 76% after the second HSCT. Three patients died from regimen-related toxicity before day 100, 9 relapsed at a median of 5.4 months (range, 1.8-34.0 months), and 12 survived a median of 9.1 years (range, 7.0-14.4 years) after the second HSCT. The Kaplan-Meier estimates of survival at 100 days, 1 year, and 10 years were 88%, 56%, and 48%, respectively. The disease-free survival rate at 10 years was 44%. Multivariate Cox regression analysis suggested that patients who received a second HSCT in relapse had a relative risk of relapse of 7.8 (P =.02) compared with patients who underwent transplantation in remission. In addition, patients who received their second HSCT </=6 months after the first transplantation were at increased risk of relapse (P =.03). These data suggest that second HSCT after a failed initial transplantation results in long-term disease-free survival in one half of children with relapsed AML. Because a higher tumor burden at the time of second HSCT was associated with a higher risk of subsequent relapse, patients might benefit from reinduction therapy before the second HSCT.