Transient myeloproliferative disorder (TMD) and subsequent acute myeloid leukemia (AML) occur with increased frequency in infants and children with Down syndrome. TMD can also occur in phenotypically normal newborns. We describe the second case of a non-Down syndrome child with TMD who subsequently developed AML. Trisomy 21 karyotypic was restricted to hematopoietic cells in the blood and bone marrow. No other karyotypic abnormalities were found. Leukemic blasts showed megakaryoblastic features with immunophenotyping. This case shows that TMD in a child without Down syndrome may not be entirely benign. Close follow-up is warranted.