Castleman's disease is a rare lymphoproliferative disease which is morphologically and clinically heterogeneous. Histopathologically it is classified into hyaline vascular, plasma cell and mixed variants and clinically into unicentric and multicentric types. Although it presents with diverse clinical and laboratory findings, as far as we know, there is no case in the literature that presents with such a marked lymphocytosis which can simulate chronic lymphocytic leukemia. In this report, a case of Castleman's disease, that is HHV- 8 positive multicentric hyaline vascular type and displaying marked lymphocytosis is presented. [Turk J Cancer 2009;39(3):110-114]