Adenomatoid tumors are benign mesothelial neoplasms most commonly found in the male and female genital tracts. Extragenital adenomatoid tumors are rare, most of them being solitary tumors. To our knowledge, only one case of multiple extragenital adenomatoid tumors, involving the liver and peritoneum, has been reported to date. Here we report another case of multiple extragenital adenomatoid tumors involving the mesocolon and omentum. A 47-year-old woman presented with a delayed menstrual period. Ultrasonography revealed a left adnexal mass, and surgical resection was attempted at a local hospital. The patient was transferred to our hospital without resection due to the intraoperative finding of multiple peritoneal tumors. At our hospital, an 8.0x7.5x6.0 cm tumor at the mesocolon of the sigmoid colon and three omental nodules measuring up to 2.5x2.0x1.7 cm were resected. Grossly, they were well circumscribed, gray-tan and elastic with small cystic spaces. Microscopically, they were composed of tubules and anastomosing channels lined by flattened or cuboidal cells with bland nuclei. Immunohistochemically, the tumor cells were positive for pan-cytokeratin AE1/AE3, vimentin, cytokeratin 5/6 and calretinin. The postoperative course was uneventful, and the patient was well 10 months after the operation. Despite their rarity, adenomatoid tumors should be included in the differential diagnosis of multiple intra-abdominal tumors.