Although the most common localization of extranodal non-Hodgkin lymphoma is the gastrointestinal system, the infiltration of the vermiform appendix is a very rare condition. We report a case of mantle cell lymphoma affecting the appendix as an incidental finding due to gynecological surgery. A 57-year-old woman presented with increasing pain in the right lower abdomen since months. During gynecological evaluation an inhomogenous mass in the right ovarian place was noticed and misinterpreted as ovarian tumor. Laparoscopic ovarectomy was planned. The intraoperative situs showed surprisingly a massive enlarged appendix and completely normal ovaries. Since the lesion was suspicious for appendiceal cancer, a right hemicolectomy was performed. Histopathology revealed a non-Hodgkin lymphoma with immunohistochemical proof of blastoid B-cells, a mantle cell lymphoma. Polychemotherapy was administered.