Within one year three patients, women aged 31, 28 and 26 years, presented with a cyclic painful small mass in the inguinal region. Histopathological examination of the resected specimen showed a pattern consistent with an extra-abdominal localization of endometriosis in the round ligament. The patients' complaints disappeared after surgical resection. It is concluded that in case of a painful mass in the inguinal region in a fertile woman endometriosis of the round ligament should be considered.