Myelodysplastic syndrome is a heterogeneous disease complex which is basically a clonal disorder and has characteristics of cytopenia of one or more cell series in peripheral blood and of dyspoiesis of precursors in bone marrow. Since the nature of this disease in childhood is very different from that in adults, retrospective clinical study was performed with 17 confirmed patients who were admitted to the Department of Pediatrics, Seoul National University Children's Hospital from June 1986 till October 1992. The results were as follows: 1) Themost frequent occurrence was found in preschool age group (76.5%), and male predominance was noted. 2) Hepatosplenomegaly was the most frequent clinical finding, and in view of laboratory findings, anemia waas found in all cases, and leukopenia in 5 cases, thrombocytopenia in 13cases were observed. Bone marrow aspiration revealed dyspoiesis of 3 cell series in almost all cases. The percentage of myeloblasts more than 5% of total bone marrow nucleated cells was seen in 8 cases on bone marrow study. 3) Subtypes of the disease were found to be 3 cases of RA, 6 cases of RAEB, 3 cases of RAEB-T, 4 cases of JCML, and 1 case of monosomy 7 syndrome. Chromosomal study was performed in 8 cases, and 6 of them were detected to be abnormal. 4) Supportive management was performed for almost all cases, and combined therapy with prednisolone and one-alpha for 3 cases, combined chemotherapy with various anticancer drugs for 7 cases, and low dose cytarabine therapy (10 mg/m2/12 hr) for 6 cases were performed. 5) There were 3 cases of drop out, 8 cases followed up on not remitted state, 5 cases of death, and 2 cases followed up on complete remission state. Two cases in complete remission were one of RA patients, and one of JCML patients, to whom prednisolone with one-alpha, and combined chemotherapy with A-Triple-V regimen were applied as treatment modalities, respectively. 6) Average duration of follow up for 10 survival cases was 18.2 months and a significant difference of 2 year survival rate was found in between the group composed of RA, RAEB and the other group composed of remained subtypes.