We report a rare case of primary malignant mesothelioma of the greater omentum. To our knowledge, only one other such case has been described in the English literature. The patient was a 61-year-old Taiwanese woman without any history of exposure to asbestos, who presented with lower back pain. Abdominal sonography and computed tomography showed a 12 x 9 x 9-cm(3) mass occupying the lower abdomen. Laparotomy revealed a tumor in the greater omentum, invading the posterior wall of the uterus, without diffuse mesenteric thickening or multiple small nodules in the peritoneum. We performed en bloc resection of the mass, which involved omentectomy, hysterectomy, and bilateral salpingo-oophorectomy. Microscopically, the tumor cells were arranged in a tubulopapillary pattern lined by a single layer of uniform, cuboidal cells. A pattern of sclerotic stroma with irregular glandular elements was also recognized. Immunohistochemically, the tumor cells showed strong positivity for calretinin. The final pathologic diagnosis was malignant mesothelioma. The patient did not receive chemotherapy or radiotherapy, and has remained in good health without any evidence of recurrence for almost 3 years since her operation.