The current case report describes the development and medical treatment of an aggressive pelvic endometrioma in a post-menopausal patient, who had undergone abdominal hysterectomy and salpingo-oophorectomy a decade earlier. The patient was referred to the authors' centre because of right-sided sciatic pain. Three months before her admission she was hospitalized elsewhere due to subacute bowel obstruction. She was operated on and a resection of a part of sigmoid colon and an endometrioma, which was the cause of the subobstruction, was carried out. During the clinical investigation for the right-sided sciatic pain, an intrapelvic mass was found, which was compressing the lumbo-sacral plexus mimicking sciatica. The diagnosis of recurrent endometrioma was confirmed by a computerized tomography-guided biopsy and the decision was made to treat it with an aromatase inhibitor (letrozole). Eighteen months later, the endometrioma was almost completely regressed and the patient was free of symptoms. Medical management of recurrent post-menopausal endometriosis with aromatase inhibitors seems to be an effective alternative treatment to surgery.