In the 12 subsep uteri the endometrium covering the septum was studied using light microscopy, electronic scanning microscopy and electronic transmission microscopy for the purpose of determining if it should be considered a reason for inadequate implantation and therefore justify an anomalous evolution of pregnancy. The results show that compared with a normal endometrium there is only a slight difference with the basal state. This alteration could however negatively influence the stages of development following implantation and particularly the structure of the maternal-fetal relationships which preclude placentation.