This report describes the first documented case of coexistent mesenteric and gonadal teratomas in an adult female patient. Physical examination of a 51-year-old Korean woman referred for treatment of abdominal distension and pain revealed two masses in both the right upper abdomen and in the right pelvic region. Computed tomography (CT) of the abdomen and pelvis showed the presence of welldefined, complex, fat-dense mass lesions in the upper abdomen and pelvic cavity. A large cystic mass located in the retroperitoneal space extending from the mesenteric border at the level of the transverse colon, and a goose-egg sized right ovarian mass were founded on exploratory laparotomy. The entire abdominal tumor was excised and total hysterectomy with bilateral salpingo-oophorectomy was performed. Examination of the macroscopic and microscopic findings led to diagnosis of mature cystic teratomas of the ovary and the mesentery. The patient's postoperative course was uneventful.