We described a case report of a 36-year-old woman with a 10-year-history of idiopathic CD4+ T-lymphocitopenia and Kaposi's sarcoma HHV8+ who developed recurrent pleural effusion. Laboratory and instrumental tests with morphologic, immunophenotypic and molecular analysis of pleural sediment suggest us the diagnosis of primary effusion lymphoma (PEL). The term primary effusion lymphoma defines an extranodal non-Hodgkin's lymphoma HHV8-related, usually classified as a B-cell lymphoma, that grows in liquid-phase within body cavities. The case reported by the Authors appears to be of great interest for its epidemiological and clinical features.