Primary intraocular lymphoma (PIOL) is a type of primary central nervous system lymphoma (PCNSL). It is the most common neoplastic masquerade syndrome involving the eye. Its protean ocular manifestations, plus in many cases the initial positive response to corticosteroid therapy for presumed uveitis, delay accurate diagnosis. A high index of suspicion is essential, followed by tissue biopsy with cytology and ancillary studies. Current treatment is based on chemotherapy featuring high-dose methotrexate and radiation therapy. Prognosis is poor due to CNS involvement, but newer therapies have had some success in prolonging survival.