- T-cell prolymphocytic leukemia is a very rare neoplasm, peaking in the seventh decade. An extensive search failed to find any report of this malignancy in the pediatric population. The malignant cell is morphologically characterized by a high nucleocytopasmic ratio, condensed chromatin, a single nucleolus, and nongranular basophilic cytoplasm. Cells are usually positive for the α/β and only rarely to the γ/δ T-cell receptors. Most patients follow an aggressive clinical course, only some respond to anti-CD52. We present a 6-year-old boy with T-cell prolymphocytic leukemia. The malignant cells expressed a postthymic immunophenotype (CD4−/CD8−) and positivity for the γ/δ T-cell receptors. The child died after 8 months despite aggressive chemotherapy, anti-CD52, and an allogeneic bone marrow transplant.