T-cell prolymphocytic leukemia (T-PLL) is an uncommon chronic lymphoproliferative disorder characterized by lymphadenopathy, splenomegaly, and lymphocytosis. The leukemic cells have the appearance of prolymphocytes and usually an immunophenotype of T-helper cells (CD3+ CD4+ CD8-). Inv(14q), del(11q), i(8q), and rearranged Xq28 are the commonest nonrandom chromosomal abnormalities in T-PLL. Recently, it has been shown that the ataxia-telangiectasia mutated (ATM) gene located at 11q23 is often deleted in T-PLL, suggesting a tumor suppressor role of the ATM gene on tumorigenesis of T-PLL. We report a case of T-PLL with t(6;11)(q21;q23) as the sole chromosomal abnormality and suggest that the cytogenetically identified translocation also implicates the ATM gene.