Primary Effusion Lymphoma is an unusual entity and it has been described as a subset associated with human herpes virus 8 infection in homosexual males with AIDS. Its inclusion as a new entity in the Revised European-American Lymphoma Classification has been recommended. The case in which it is presented is a 47-year-old man, diagnosed with AIDS two years ago, who came with Kaposi's sarcoma. Nowadays, he has a right pleural effusion and a thoracentesis has been carried out. We obtain 10 ml of haemorrhagic fluid which is processed by standard methods. The morphologic study reveals a non-Hodgkin's lymphoma of high-grade. The immunophenotypic study shows a lymphoid neoplasm of indeterminate lineage and high proliferation index. It confirms the HHV-8 in the neoplastic cells by PCR. The diagnosis is a non-Hodgkin's lymphoma of high-grade compatible with Primary Effusion Lymphoma.