T-cell prolymphocytic leukemia is a rare and unusual malignancy characterized by the proliferation of small- to medium-sized prolymphocytes of postthymic origin with distinctive clinical, morphologic, immunophenotypic, and cytogenetic features. Involvement of the peripheral blood, bone marrow, lymph nodes, liver, spleen, and skin can occur. The clinical course is typically very aggressive with poor response to conventional chemotherapy and short survival rates, and the only potential long-term curative treatment is hematopoietic stem cell transplantation. We report the case of a man with de novo T-cell prolymphocytic leukemia and discuss the distinctive clinical, morphologic, immunophenotypic, and cytogenetic features of this entity.