Intraocular central nervous system (CNS) lymphoma represents a diagnostic challenge and is often misdiagnosed as uveitis or vitritis.1,2 Establishing the diagnosis requires a high index of suspicion based on the clinical findings, followed by identification of malignant lymphocytes in vitreal or cerebrospinal fluid specimens. Although vitreous cytology is a sensitive, reliable, and reproducible method in experienced hands,3 the possibility of false-negative results is considerable, particularly owing to the paucity of malignant lymphocytes amongst reactive lymphocytes in specimens, inappropriate handling, and incorrect interpretation. Therefore, the search for a highly specific and sensitive diagnostic test has continued.