A study was undertaken to assess the natural history of periocular lymphoproliferative diseases, identify key prognostic factors, and clarify the role of orbital irradiation. Thirty-four patients with periocular lymphoproliferative disease were treated with orbital irradiation between 1975 and 1990. Eight patients had atypical lymphoid infiltrate, and 26 had malignant lymphoma. Forty-three eyes were irradiated with en-face electrons or 6-MV photons. Five-year disease-free survival for all stages was 65%; it was not significantly affected by bilaterality or site. Stage, distinction between atypical lymphoid infiltrate and malignant lymphoma, and working formulation grade were important prognostic indicators. A complete response during irradiation was achieved in 24 of 43 (56%) eyes at a median dose of 2,400 cGy, and a partial response was achieved in 19 (44%), with resolution at a median of 2.8 months. Patients with periocular reactive lymphoid hyperplasia or atypical lymphoid infiltrate may have or are at significant risk of developing lymphoma and dissemination. Local treatment remains important; orbital irradiation achieves prompt local control with acceptable morbidity.