A 29-year-old male with acquired immunodeficiency syndrome presented with a week of left eye blurriness, which then progressed to complete vision loss. On exam, the left pupil was nonreactive to light, and fundoscopy showed significant optic nerve edema. CT and MRI of the left orbit showed a mass lesion compressing the posterior aspect of the sclera with diffuse thickening and contrast enhancement of the retrobulbar portion of the left optic nerve. The lesion demonstrated low T1 and intermediate T2 intensities and heterogeneous contrast enhancement and measured 17.4 mm x 15 mm x 10.6 mm. Anterior orbitotomy with exploration and biopsy were performed. Immunohistochemical studies confirmed diffuse large B-cell lymphoma and a workup showed no systemic involvement. Plans for treatment with chemotherapy and radiation were initiated. Even though rare, primary orbital NHL should be in the differential for relatively acute blindness without other symptoms, especially in patients with AIDS.