A case is presented of CD30+ anaplastic large cell lymphoma of the spleen. The patient, a 61 year old woman with a history of chronic lymphocytic leukemia (CLL) was seen for the sudden development of splenomegaly with thrombocytopenia. A splenectomy was performed which showed massive replacement of the spleen by a population of large atypical lymphoid cells showing bizarre nuclear forms and multinucleated tumor cells reminiscent of Reed-Sternberg cells. Immunohistochemical studies showed strong membrane and dot-like paranuclear positivity in the majority of the atypical cells for CD30, with coexpression in many of the cells for CD15. Additionally, the cells also strongly reacted with CD3, UCHL-1, EMA and LCA. The present case illustrates an unusual variant of anaplastic (CD30+) large cell lymphoma sharing histologic and immunophenotypic features that overlap with those of Hodgkin's disease. The history in this patient of CLL with sudden development of splenomegaly raises the possibility of transformation of CLL into a high-grade lymphoma (Richter's syndrome). The possible pathogenetic implications of this phenomenon are discussed.