T-cell prolymphocytic leukemia is a rare postthymic malignancy with distinctive clinical, morphologic, immunophenotypic, and cytogenetic features. The clinical course is typically aggressive with poor response to conventional chemotherapy and short survival. Treatment with purine analogues and alemtuzumab has resulted in significantly higher response rates and improved survival. Nevertheless, responses are relatively short, and the only potential curative treatment is allogeneic stem cell transplantation. The age and comorbidities of many of the patients has limited this option, but the growing use of nonmyeloablative transplantation has now widened the patient eligibility for this approach.