SIGNIFICANCE: Plasmablastic lymphoma (PBL) involving the ocular adnexa, although reported in the literature, is a rare clinical entity, especially when found in an immunocompetent patient. Understanding the clinical presentation can aid eye care practitioners in seeking timely diagnosis to avoid further delays in the treatment of this disease.PURPOSE: This study aimed to report orbital PBL in an HIV-negative patient and discuss the presenting clinical signs, symptoms, and other diagnostic findings for the proper treatment and management of this condition. CASE REPORT: A 79-year-old White male presented to our clinic for a second opinion for the evaluation of a swollen, mildly painful right eye for 2 months. The patient also complained of intermittent tenderness of the right frontal and paranasal sinuses. The initial diagnosis was preseptal cellulitis. Best-corrected visual acuity was 20/40 in the right eye and 20/30 in the left eye. A thorough comparison of the globe revealed subtle proptosis in the right eye. Slit-lamp evaluation revealed severe conjunctival chemosis, which was greatest in the inferotemporal quadrant, and diffuse right inferior eyelid edema. Globe proptosis was quantified via Luedde Exophthalmometer (Gulden Ophthalmics, Elkins Park, PA). Exophthalmometry values were 22 mm in the right eye and 20 mm in the left eye, suggesting mild proptosis of the right eye. MRI of the brain and orbits revealed an expansile lesion in the right maxillary, ethmoid, and paranasal sinuses. The mass also extended into the anterior cranial fossa and the right orbit. Needle biopsy and immunohistochemical analysis confirmed a diagnosis of PBL. The patient chose to discontinue chemotherapy owing to adverse systemic effects and died of the disease 36 months after the initial diagnosis. CONCLUSIONS: Unilateral conjunctival chemosis with no improvement or resolution warrants further investigation and workup. Eye care practitioners play a crucial role in the diagnosis and management of these patients in close collaboration with pathology, hematology, and oncology specialists.