Cystic mesothelioma of the peritoneum is a very rare tumor which has a clinically and histologically benign nature. It occurs predominantly in young to middle-ged women and tends to recur locally. It affects chiefly the pelvic peritoneum-articularly the cul-e-ac, uterus, and rectum. We report a case of cystic mesothelioma of the visceral peritoneum which was located anterior to the ascending colon. A 54-ear-ld female patient visited our hospital with a palpable tender mass in the right flank. A computed tomographic scan of the abdomen showed a multicystic mass with an enhancing wall and septum in front of the ascending colon. The patient underwent a right hemicolectomy, and the mass was completely removed. Grossly, the tumor consisted of a multilocular cyst containing clear, serous, or gelatinous fluid and partially solid areas. Microscopically, the solid areas were composed of fibrous tissue, and the lining cells varied from flattened to cuboidal cells with a strong positive reactivity for cytokeratin and mild positive reactivity for epithelial membrane antigen on immunohistochemical staining. These findings suggest that the tumor was mesothelial in origin.