Mesothelioma is a rare neoplasm originating from the surface of the mesothelial cells of the serous membranes, mainly of the pleura and peritoneum. We report the case of a malignant peritoneal mesothelioma found inside an incarcerated abdominal hernia in a 90-year-old woman with no history of asbestos exposure. She was surgically treated by routine herniorrhaphy, and examination of specimen pathology revealed the presence of neoplasia in the hernial sac. In addition, the patient had colonic diverticulosis. It leads to consider the importance of pathological evaluation of routine surgery specimens as they could be compatible with the incidental diagnosis of neoplasms.