We describe a 7-year-old girl with therapy-related acute myeloid leukemia (AML) associated with a single and novel karyotypic abnormality. The patient had been treated with alkylating agents and etoposide for hypothalamic pilocytic astrocytoma at age 17 months, and developed mixed lineage AML. Cytogenetic analysis of the leukemic blasts showed 46,XX,der(7)t(7;11)(q22;q14) in all cells examined. Southern blot analysis revealed three copies of an unrearranged MLL gene on chromosome 11q. This is the first report of a triplicated, unrearranged MLL gene in association with a deletion of 7q anomaly and an unbalanced translocation in therapy-related leukemia.