A 34-year-old woman had a progressively protruding and painful mass of the right orbit for 1 month. On examination, the soft-tissue mass was about 5 cm in diameter and firmly fixed to the right orbit with resultant protrusion of the lower eyelid and proptosis (Figure 1A and B). Visual acuity was no light perception, coupled with limited eyeball motility. There was neither hepatosplenomegaly nor lymphadenopathy. Her family history was noncontributory. Computed tomography of the orbits revealed a large mass measuring 7.1 × 4.9 × 4.8 cm and completely occupying the expanded right orbit without bony destruction (Figure 1C). Magnetic resonance imaging of the orbits showed a large, heterogeneously enhancing soft-tissue mass compressing and pushing the eyeball anteriorly and extending posteriorly to the optic canal (Figure 1D). A small incision was made through the superotemporal conjunctiva and Tenon capsule, where tumor cell invasion with a cicatrizing nature was identified and incised. Histopathological analysis of orbital biopsy specimens demonstrated atypical lymphoid cell infiltration with positive immunoreactivities for CD3 and CD2 (Figure 2). The neoplastic cells were negative for CD56, CD15, CD30, and latent membrane protein 1 (Figure 3). Evaluation of T-cell receptor gene rearrangement using polymerase chain reaction showed monoclonality over the T-Cell receptor γ chain gene, consistent with peripheral T-cell lymphoma (Figure 4A). Staging fluorine 18 (18F)-labeled fluorodeoxyglucose positron emission tomography showed lesions with striking 18F-fluorodeoxyglucose uptake over the right ortibal region without evidence of hepatic, splenic, or lymph node involvement, supporting the diagnosis of primary peripheral T-cell lymphoma of the orbit (Figure 4B and C). At the 3-month follow-up, the patient refused to receive chemotherapy but completed radiotherapy. Proptosis and the protruding mass in the right eye failed to achieve satisfactory resolution.