The indolent course of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) is occasionally altered by transformation to a histologically distinct, rapidly progressive, and clinically unresponsive hematologic malignant neoplasm. We report a case of CLL that, after 3 years of slowly progressive disease and treatment with single-agent chemotherapy (fludarabine phosphate), underwent a composite prolymphocytoid and classic Hodgkin lymphoma transformation. The diagnosis of classic Hodgkin lymphoma was based on the presence of Reed-Sternberg cells with typical morphologic structure and immunophenotype (CD15(+), CD30(+), CD45(-), CD20(-)) associated with the characteristic polymorphous inflammatory background consisting of numerous eosinophils, plasma cells, and reactive T lymphocytes. The remainder of the lymph node and the peripheral blood showed increased numbers of prolymphocytes admixed with typical small CLL cells. Recognition of such a transformation is of the utmost importance, since histologically similar Reed-Sternberg-like cells may be seen in Richter transformation. In contrast to prolymphocytoid transformation of CLL, Richter syndrome is rapidly fatal, with a median survival of 4 to 5 months. The patient pursued a clinical course similar to pure prolymphocytoid transformation and died with disease after 30 months following treatment with combination chemotherapy.