Endometriosis is not a well-known disease and sometimes its rare onset is a pathogenetic, diagnostic and therapeutic problem. The Canal of Nuck is an embryonal rest of the parietal peritoneum that accompanies the round ligament through the inguinal canal. The perviousness of the canal of Nuck could explain the pathogenesis of vulvar endometriosis.We reported a case of vulvar endometriosis localization, which is rather uncommon, in a patient previously operated on with cyst of Nuck.One of the most helpful instrumental exams in defining the nature of vulvar swallows is magnetic resonance, but it remains difficult to diagnose vulvar endometriosis in spite of the instrumental exam in our possession. The hypothesis of retrograde menstruation is supported by the fact that ovarian localization is the most common in this disease. Extra-pelvic localization as well as vulvar one are less common. The Canal of Nuck is an embryonal rest of the parietal peritoneum that accompanies the round ligament through the inguinal canal.Endometriosis could be taken into consideration in differential diagnosis of vulvar swellings, and for this reason it is necessary to carry out a histological exam in every operated vulvar neoformation. We suggest vaginalis-peritonei duct contamination as a possible pathogenesis mechanism of this disease.