Three cases of endometriosis infiltrating the round ligament are presented. The initial diagnosis was irreducible hernia, since this rare nosologic entity often causes unusual preoperative symptoms and diagnostic problems. Diagnosis is frequently made by histologic examination. The rarity of inguinal endometriosis should not exclude it from a possible diagnosis in cases with a painful mass in the inguinal region in a fertile woman, especially if the groin mass is associated in size and tenderness with menstrual variability. Surgery is the treatment of choice and is curative; laparoscopy is suggested during the same operation to evaluate the intraperitoneal conditions.