Today, due to modern interdisciplinary treatment, more than half of all children with malignancies are expected to be long-term, relapse-free survivors. While most of these will lead normal lives, some will suffer from therapy-related late effects, which may even be life-threatening in some cases, e. g., symptoms of severe cardiomyopathy, often refractory to medical intervention, may develop after anthracycline therapy. Subclinical cardiac damage is disturbingly frequent. The development of secondary malignancies can be favoured by individual predisposition as well as radiation therapy and several cytostatic agents. Nephro- and ototoxicity as well as endocrine abnormalities may be irreversible. Severe CNS damage can follow treatment for brain tumors. While fertility can be impaired by cancer therapy, it is frequently unaltered. Children born to parents who were previously treated for cancer usually do not have an increased risk of deformity or malignancy. A late effects group has been formed within the ''Gesellschaft fur padiatrische Onkologie und Hamatologie'' (GPOH). This group investigates the incidence and severity of therapy-related late effects in order to be able to make suggestions concerning possible modifications of primary treatment and concerning long-term follow-up.