Introduction: Primary ovarian lymphoma may present with a clinical scenario consistent with advanced epithelial ovarian carcinoma. Although ovarian lymphoma is a rare entity, accounting for 0.5% of all non-Hodgkin’s lymphoma and 1.5% of all ovarian neoplasms, it should be included in the differential diagnosis of an ovarian mass. Case: We report a case of a 78-year-old woman who presented with an ovarian neoplasm suggestive of advanced ovarian carcinoma. During diagnostic laparoscopy, biopsies were obtained with frozen section analysis revealing malignant lymphoma. Further histopathologic analysis revealed a diffuse large B-cell lymphoma (DLBCL). The treatment plan was for six cycles of R–CHOP chemotherapy. A drammatic response was noted after only three cycles of R-CHOP. Conclusion: Primary ovarian lymphoma presenting as an ovarian tumor is exceedingly rare. Since the prognosis and treatment of lymphoma differs significantly from ovarian carcinoma, a representative tissue sample of the adnexal tumor should be obtained and sent for frozen section analysis to establish the diagnosis. Principal treatment for non-Hodgkin’s lymphoma is chemotherapy without surgical cytoreductive efforts.