BACKGROUND: The myelodysplastic syndromes (MDS) in childhood is considered to be very rare and the nature of this disease in childhood is very different from that in adults. We analyzed the hematologic findings of childhood myelodysplastic syndrome. METHODS: The retrospective study was performed with the confirmed patients who were admitted to the Department of Pediatrics, Asan Medical Center (AMC) from June 1989 till May 1999, to analyze the hematologic findings. Sixteen children with a primary myelodysplastic syndrome (MDS) were presented to AMC during a 10 year period. RESULTS: Morphological assessment of the peripheral blood and the bone marrow showed nine patients (56%) had refractory anemia (RA), two patients (13%) had RA with excess blasts (RAEB), five patients (31%) had RAEB in transformation (RAEB-t). Five children with juvenile chronic myelogenous leukemia were diagnosed over the same period. Age distribution showed the predilection between 6~10 years and male : female ratio was 1 : 1. Inperipheralblood, pancytopenia was found in seven cases (44%) and leukocytosis in four cases (25%). The bone marrow findings showed hypercellularity in 54%, hypocellularity in 8% and variable cellularity in 15% and myelofibrosis was observed in 23%. Various dyspoietic changes of erythrocytes, leuko- cytes and platelets in peripheral blood and three cell lines in bone marrow were observed and trilineage dysplasia was observed in 62% of MDS, and 56% of RA. The four cases (25%) of RAEB and RAEB-t have transformed to acute myelogenous leukemia. CONCLUSION: In our study, the MDS in childhood seemed to be characterized by higher incidence of RA. Compared with the adult MDS, trilineage dysplasia in RA was frequently seen, but, no significant differences of dyspoietic features between adults and childhood were observed.