The initial findings and the course of 20 children and adolescents with adult CML from 10 children hospitals were analyzed retrospectively. The Philadelphia chromosome was found in 18 patients. Initial findings, the course and the prognosis were similar to those published from adult patients. 7 of the 11 children who received chemotherapy alone are still alive with a median survival time of 26 months (range: 14 to 68 months). One patient survived the third blast crisis. For 9 children with a bone marrow transplantation during the chronic phase (median time before transplantation 30 months) the follow-up of 7 months is still too short. 4 of these patients died following graft versus host reaction, 5 show no signs of a renewed occurrence of CML so far. Since CML is rare in children, there is little large scale experience. Hence, there is an urgent need for the prospective and cooperative study of these patients.