Six cases with a coexistence of endometriosis and genital anomalies among 112 patients with external endometriosis and 90 patients with genital anomaly were detected. Three cases of severe endometriosis associated with uterovaginal duplication, unilateral renal agenesis and ipsilateral blind vagina and the latter in a patient with Rokitansky-Kuster-Hauser syndrome are presented. Another case with obstructive genital anomaly without endometriosis is also presented. The histogenetic mechanisms of endometriosis are discussed. The transplantation theory is not sufficient to explain all the cases and, therefore, the theory of celomic metaplasia and the theory of müllerian remains or Cullen’s theory, as well as the intervention of genetic-constitutional, immunologic, hormonal and other factors must also be consider