A 45-year-old woman, gravida 2 para 1, who had had a normal vaginal birth and no dysmenorrhea before, presented to our emergency department with sudden onset of pelvic pain. Abdominal and pelvic computed tomography revealed multilobulated, glove-like nodules on the fundus of the uterus (Fig. 1). Laboratory tests revealed an elevated CA-125 (355.1 U/mL, normal range: Fig. 2). The pathology report revealed typical endometrial glands with focal hemorrhage (Fig. 3A) and stroma arising from the subserosal part of the uterus (Fig. 3B). After the operation, the patient recovered uneventfully and was discharged without any complications. Oral progesterone has been prescribed for the treatment of residual peritoneal endometriosis. Her CA-125 level returned to normal three months after the operation.