This is a survey of all the 265 relapses occurring in 515 children with ALL diagnosed in Sweden in the years 1973-1980. Two hundred and nineteen relapses occurred on therapy, and 46 after discontinuation of therapy. Bone marrow was involved in the relapse in 71% and 67% of the two groups, respectively. Only 38/265 (14%) children with relapse were still alive at follow-up in January 1985. Of these, 16/219 (7%) had relapsed during therapy (median survival time after relapse 9 months) compared to 22/46 children (48%) with a relapse after cessation of therapy (median 43 months). The prognosis was better if relapse occurred after cessation of therapy and in children with isolated testicular relapse. Thirteen children were bone marrow transplanted, and 6 of these were alive at follow-up. It is concluded that children with ALL relapse have very bad prognosis with cytostatic regimens used today, especially if the bone marrow is involved.