Cystic mesothelioma is a rare tumor of the peritoneal cavity arising from mesothelial cells. About 130 cases have been reported in the literature. The tumor is more frequent (85%) in adult women and rarely occurs in children. It is benign but recurrences are often described. The differential diagnosis with adenomatoid tumors, lymphangiomas, cystic malignant mesotheliomas and metastatic serous cystic tumors of the ovary is supported by immunohistochemistry. We describe four cases of cystic mesothelioma of the peritoneum; two of the cases occurred in pregnant women, one in a 45-year-old man and one in a 5-year-old boy. Asbestos exposure was not documented. The mesothelial origin of the neoplasms was supported by immunohistochemical analysis. Furthermore, tests for simian virus 40 (SV40 T antigen), to determine whether this virus was also present in the lesions, were negative.