The authors performed histopathological and immunohistochemical studies of 14 cases of orbital malignant lymphoma except for the conjunctival one. The patients were composed of 9 males and 5 females, and the average age of the cases was 61.5 +/- 12.3 years old. All cases were unilateral malignant lymphomas, 5 cases were right and 9 cases were left. Two patients had stage I disease, 10 patients had stage II disease, and 2 patients had stage III disease. The 5 year-survival rate was in 7/12 (58%). Histopathological examination revealed that 3 cases belonged to small lymphocytic, 4 cases diffuse small cleaved, 3 cases diffuse mixed and 4 cases diffuse large cell type by the working formulation. Immunohistochemical examination showed that all cases reacted positively against the B cell markers, while negatively against the T cell markers except for 1 case, indicating the cases were B cell lymphomas. Additionally, an immunoglobulin study contributed to elucidate the monoclonal proliferation of the tumor cells.