We identified 2 cases of secondary acute myeloid leukemia (AML) following adult T-cell leukemia/lymphoma (ATL) in patients who had previously received chemotherapy. Both cases were thought to represent therapy-related AML because the patients had previously received combination chemotherapy including epipodophyllotoxin, anthracycline, and alkylating agents for the ATL. The cases were diagnosed as AML M4 with eosinophilia and AML M2, with the chromosomal abnormalities inv(16)(p13q22) and t(8;21)(q22;q22), respectively. In our hospital, only these 2 cases of secondary AML accompanying ATL were identified among 90 cases of acute- or lymphoma-type ATL diagnosed from October 1999 to July 2006. The frequency of coexisting AML and ATL is lower than that reported for acute leukemia coexisting with other lymphoid malignancies. The low frequency of secondary leukemia with ATL may be associated with the short survival times of ATL patients.