The authors report two cases (in brothers) of the persistence of Muller's ducts (uterus and uterine tubes), whilst both individuals led a normal though infertile sex life. They presented with a bilateral inguinal hernia and a cryptorchidism. The precise diagnosis was made at surgery in the first, whilst the family history led to the diagnosis in the second. Both underwent bilateral orchidopexy, and hysterectomy with excision of the uterine tubes. The caryotypes were normal. Of anatomical interest was the fact that both had vas deferens included within the uterine wall but the there was no continuity between the epididymes and the testes. The latter contained seminiferous ducts, Sertoli cells and spermatogonia but no spermatocyte nor spermatozoa. On the basis of these cases, the authors emphasise their demonstrative nature: the presence of testes resulted by the secretion of testosterone in the induction of normal external genitalia whilst the absence of factor inhibiting Mullers ducts (or tissue resistance to this factor) resulted in the development of the uterine tubes and uterus.