From 1983 to 1988 14 patients under 16 years of age with adult type chronic myelogenous leukemia (CML) in chronic or blastic phase were treated by allogeneic bone marrow transplantation (BMT) in our center. These comprise 54% of all patients under 16 years of age grafted for this disease in FRG. These BMT patients were compared with 24 similar patients treated conventionally with busulfan and/or hydroxyurea in various centers. The probability of an event-free survival 5 1/2 years after BMT was 0.61 (SD 0.16); the estimated probability of survival for 3-8 years after diagnosis in the group treated by GMT was 0.78 (SD 0.14) vs 0.55 (SD 0.12) for the non-BMT group. The difference is not significant. In the BMT group only two patients died of transplant-related complications. The non-BMT patient with the longest survival period died recently 10 years after diagnosis. For children with adult type CML, BMT is a safe and effective treatment, and should be recommended if there is an HLA compatible sibling donor or even a fully compatible unrelated donor. However, for a more conclusive comparison between bone marrow transplantation and conventional treatment a longer observation period and larger patient numbers are necessary.