Near-tetraploidy is a rare cytogenetic abnormality in myelocytic malignancies in children, and its significance is unknown. To investigate the characteristics of near-tetraploidy in a child with acute myelogenous leukemia (AML-M4), bone marrow smears were prepared for morphological analysis. Bone marrow samples were collected for flow cytometry, and prepared by short-term (24 hrs) unstimulated culture and R-banding for conventional cytogenetic assay. In this case, the morphological analysis of bone marrow cells showed large and prominent nuclei. The chromosomal analysis (R-banding) demonstrated a near-tetraploidy. Combined with morphological and immunophenotypic results, AML-M4 was confirmed. The patient was given four cycles of chemotherapy, and finally achieved clinical remission. However, the duration achieving the remission in the child was longer than AML children with normal karyotype. It is believed that near-tetraploid karyotype may have a great significance to the therapy and prognosis.