Childhood MDS comprises a group of heterogeneous clinical disorders with overlapping features and many similarities to adult MDS. Environmental factors, genetic predisposition, certain viral infections, and impairment of the developing immune system perhaps play a major role in the genesis of the most common disease forms, such as JCMMoL and the monosomy 7 syndrome. One intriguing finding in these disorders is the striking male predominance. Diagnostic difficulties occur because dysplastic manifestations of the hematopoetic systems are usually not as impressive as in adults and because myelodysplastic and myeloproliferative disease forms overlap considerably. Despite these problems, we believe that pediatric cases of MDS should also be classified according to the established FAB classification for MDS. However, as has already been proposed earlier by others, JCMMol clearly should be considered as a specific entity different from the adult form of CMMoL. As has been shown by cell culture studies, JCMMoL is characterized by the presence of neoplastic macrophage/monocyte progenitor cells. These cells produce several factors that result in autostimulation and suppression of normal hematopoiesis. MDS is a highly malignant disease in children and evolves to acute leukemia after a short period. During the early phase of the disease, supportive care is sufficient. If a compatible donor is available, BMT is the treatment of choice and should be performed during the early stage of disease progression after clinical remission is obtained with chemotherapy. If BMT is not feasible, intensive chemotherapy may improve the clinical condition and prolong survival. Preliminary data suggest that the incorporation of hematopoietic growth and/or differentiation factors in chemotherapy and BMT protocols may have some beneficial effects. The only way to accumulate sufficient data on MDS in children with respect to clinical features, prognosis, and efficacy of treatment is to follow a uniform diagnostic and treatment program. To achieve substantial improvements in the management of childhood MDS, multicenter trials will be essential.