The FAB group has defined myelodysplasia in adults but direct application of this categorization to children has been controversial. Consequently, to outline the natural history of the disease better we have retrospectively analysed case reports and series published in English between 1982 and 1996. This study also included children with juvenile chronic myelomonocytic leukaemia (JCML) and monosomy 7 (Mo7). 340 patients were described in 27 publications. The mean presentation age was 5.91 (SD 5.04) years, and 34.9% were female. Constitutional alterations were described in 68 (20%) where refractory anemia (RA) and RA with excess of blasts (RAEB) predominated and were associated with a significantly longer survival. Among all patients progression to higher forms of MDS was noted in 61 (18%). Cytogenetic anomalies were detected in 59% of 227 children, and in 67 it was to Mo7. Amid those with Mo7, the clinical and laboratory characteristics as well as survival, closely followed their FAB type. Of the treatment options described, survival was significantly higher in those who underwent bone marrow transplant (BMT) (46.9%; P = 0.00021). Among children with JMML (CMML/JCML) not receiving a BMT, time to death was shortest in those best described as JCML (absence of constitutional and karyotypic derangement, thrombocytopenia and elevated Hb F). We conclude that children with constitutional abnormalities survive longer, Mo7 disorders are clinically and morphologically heterogeneous and should not be grouped into a single entity and that CMML and JCML may have biological differences. Finally, BMT remains the treatment of choice for those with primary MDS, as intensive chemotherapy is no better than supportive measures. Am.