[en] We have reviewed 37 patients with primary orbital lymphoma, using the Ann Arbor criteria and the Working Formulation and its modification. Thirty-one patients had stage I disease, four stage II, one stage III and one stage IV. The male to female ratio was 2.7:1. There were 34 low-grade tumours (including 24 mantle zone) and three intermediate-grade. Patients were divided into three groups according to their primary treatment. Group 1: radiotherapy (17 cases); Group 2: surgery alone (13 cases); Group 3: chemotherapy (seven cases). Patients were followed up from 5 months to 24.3 years, with a mean and median of 7.6 and 6.2 years, respectively. The BMDP software package was used for survival estimation (Kaplan-Meier) and determination of prognostic variable (univariate Cox regression). Local relapse-free survival at 10 years was 100% in Group 1, 0% in Group 2 and 42% in Group 3 with a statistically significant difference (p < 0.01) in favour of radiotherapy. Statistically significant good prognostic features were: complete remission (CR) in response to initial treatment, primary radiotherapy and older age. For stage I cases, there was no difference in distant relapse-free survival in the three groups. The overall cause-specific survival for stage I patients at 10 years was 100% for each group and at 20 years was 100, 67 and 0% for Group 1, 2 and 3. The difference between the primary radiotherapy and chemotherapy-treated groups was significant at the p = 0.08 level. Statistically significant prognostic factors were early stage, low-grade histology and primary radiotherapy. In one patient, ptosis and diplopia appeared after surgery. One case of glaucoma required enucleation, one patient suffered severe dry eye syndrome. All patients ((11(11))) in whom the lens received direct radiation developed cataracts of different degrees if follow-up was long enough. Cataract formation was prevented by adequate lens shielding. One patient in CR from a stage I low-grade tumour died from chemotherapy-induced marrow aplasia. Primary orbital lymphoma is an indolent, usually stage I disease, showing low to intermediate-grade histology. After biopsy the best treatment is 30 (low-grade) to 40 Gy (intermediate-grade) carefully planned, lens-sparing megavoltage radiation without adjuvant chemotherapy