Endometriosis is a benign, estrogen-dependent condition that commonly affects women during the reproductive age. Postmenopausal endometriosis is a rare condition because of the absence of estrogenic hormone production. Furthermore, extrapelvic endometriosis is a rare and complex phenomenon. For this reason, it is usually a misdiagnosed disease. An 84-year-old female patient with no medical history of endometriosis or dysmenorrhea and no hormone replacement therapy was found to have a 4.4×3 cm tender, mobile mass on the left labium majus detached from the underlying perineal muscle. The patient underwent surgical excision under sedation and local anesthesia. The mass was easily removed intact and was not adherent to the vagina or the perineal muscles. Surgical resection of the lesion should be performed in order to remove the lesion and to confirm the diagnosis histologically. The diagnosis of long-standing endometriotic cyst was made. Primary vulvo-perineal endometriosis is a rare and difficult diagnosis especially in postmenopausal women without previous surgical procedures and no history of endometriosis. A better awareness of symptoms and signs of uncommon locations of extrapelvic endometriosis should be encouraged in order to optimize patient care. Finally, more research is needed to elucidate the pathogenesis of endometriosis in postmenopausal women.