Although treatment of childhood acute myelogenous leukemia (AML) has substantially improved in the last 15 years, in nearly half of the patients disease recurs. The aim of this study was to establish the prognosis of relapsed childhood AML and to identify prognostic factors for achievement of second remission and survival. From February 1988 to July 1996, 134 children with first relapse of AML were reported to the study center of the AML-BFM group. 102 patients treated intensively to induce second remission were prospectively followed. With various regimens, complete remission was achieved in 52 of 102 patients (51%), 27 children were alive in median 2.5 years (range, 0.4-7 years) after relapse. Disease-free survival was observed in seven of 16 patients transplanted from a matched sibling donor, one of four after matched unrelated bone marrow transplantation, 10 of 22 after autologous transplantation and five of nine patients after chemotherapy alone (two patients were lost to follow-up). Time until relapse reflecting the duration of first remission is the only variable correlating CR and survival rates. Defining early relapse as less than 1.5 years from diagnosis to relapse resulted in a 5-year survival of 10%, s.e. 5% for early relapses and 40%, s.e. 10% for late relapses (P-logrank test, 0.0001). Duration of first remission is a strong predictor for achievement of second CR and survival. It should be considered in reporting results of experimental therapies.