An analysis of non-Hodgkin's lymphoma involving the orbital structures was performed at the University of Iowa between 1937 and 1975. Sixteen cases of primary orbital lymphoma were diagnosed. Histopathologic reclassification according to the Rappaport scheme and the clinical course of each histologic sub-category was described. There were 5 patients with reactive hyperplasia, 2 patients with well-differentiated lymphoid proliferation with Dutcher bodies which were also felt to be reactive, 3 patients with diffuse poorly differentiated lymphocytic lymphoma, 4 patients with nodular poorly differentiated lymphocytic lymphoma, and 2 patients with diffuse histiocytic lymphoma. It was concluded that the Rappaport classification is applicable to orbital lymphoid tumors and that those lymphomas which do present as primary tumors should be staged as one would stage the same histologic category of lymphoma presenting in other sites. Radiation therapy appears to be an effective treatment for local control; however, patients with primary orbital lymphoma should undergo observation for systemic disease similar to patients with lymphoma presenting in other sites. Excisional biopsy is recommended to facilitate precise classification.