To define the role of radiation therapy of primary orbital lymphoma, a retrospective analysis was undertaken for 18 patients with primary orbital lymphoma who were treated with curative radiotherapy between 1984 and 1995. The histology was found to be low grade lymphoma in 11 patients, intermediate grade in 7. All patients were of Ann Arbor stage IE, but bilateral involvement of the orbit was observed in 3 patients (16.6%). Anatomical subsites involved were the retrobulbar, eyelid, and conjunctiva in eight, five, and four patients, respectively. The median radiation dose was 30 Gy ranging from 20 Gy to 50 Gy. Twelve of 18 patients received a radiation dose of 30 Gy or less. To properly protect the lens during irradiation, the contact lens blocks were used for nine patients with conjunctival and eyelid tumor or the hanging eye bar blocks were applied for eight patients with retrobulbar tumor. Chemotherapy was given for seven patients with intermediate-grade malignant lymphoma. Two patients had been treated by surgery before referral.