Primary effusion lymphoma (PEL) in patients with Human Immunodeficiency Virus (HIV) infection may involve pleural, pericardial, and peritoneal cavities. PEL involving the cerebrospinal fluid (CSF) is exceedingly rare, and to our knowledge has only been reported in two cases. We report another case of PEL diagnosed in CSF from a 61-year-old male with Acquired Immunodeficiency Syndrome that presented with neurological symptoms. Imaging studies of his brain showed leptomeningeal/periventricular enhancement, but no mass lesion. His CSF demonstrated human herpesvirus-8 positive pleomorphic lymphoplasmacytoid cells of null cell phenotype. This case highlights that albeit rare, PEL should be included in the differential diagnosis when large atypical cells are encountered in CSF of HIV-positive patients, even when such patients have no history of lymphoma. As in this case, ancillary studies are required to make an accurate diagnosis of PEL in CSF cytology.