In this report, we describe a patient with Philadelphia chromosome-negative chronic myelogenous leukemia (CML) with breakpoint cluster region gene rearrangement who developed T-cell lymphoblastic lymphoma. The occurrence of T-cell lymphoblastic lymphoma coincided with the appearance in the bone marrow of the cytogenetic abnormality, trisomy 22q11.2----22qter. This is the first report of high-grade T-cell lymphoma in a patient with documented CML.