In this report, we describe our experience with high-dose chemotherapy (HDC) and autologous stem cell transplantation (ASCT) in 15 children with relapsed osteosarcoma who were treated by members of the Cooperative Osteosarcoma Study Group. Eight patients received HDC after the first relapse, six patients after the second relapse and one after the sixth relapse. Thirteen patients underwent HDC and ASCT in complete remission and two patients had macroscopic tumor residues. Seven patients received HDC based on melphalan and etoposide. Four of these patients were treated with additional carboplatinum. Two patients received carboplatinum, etoposide, and thiotepa or cyclophosphamide. In six patients double HDC was performed. In all six of these, the first HDC consisted of thiotepa/ cyclophosphamide. The second regimens included melphalan/etposide (two patients), melphalan/etposide/ carboplatinum (one patient), and melphalan/busulfan (one patient). Three of the 15 patients died of toxic complications. Eight patients developed further relapses, two patients showed persistent disease, and two patients are presently in continuous complete remission. The probability of relapse-free survival was 0.20 +/- 0.12 within a median follow-up (MFU) of 8 months and the probability of overall survival was 0.29 +/- 0.12 after a MFU of 16 months. In conclusion, utilization of HDC and ASCT in this patient group did not significantly improve the treatment outcome compared to conventional relapse therapy.