Thirty-seven children and adults who developed acute nonlymphocytic leukemia after the administration of chemotherapy that included etoposide or teniposide for a variety of hematologic and solid malignancies were identified. The secondary leukemia that occurred in these patients could be distinguished from the secondary leukemia that occurs after treatment with alkylating agents by the following: a shorter latency period; a predominance of monocytic or myelomonocytic features; and frequent cytogenetic abnormalities involving 11q23. Patients receiving an epipodophyllotoxin are at risk for developing secondary leukemia that has features distinct from the syndrome of secondary leukemia associated with alkylating agents.