Two cases of acardius were observed by the authors among nearly twenty thousand deliveries in the seven year period of the 1st Department of Obstetrics and Gynecology, between 1990 and 1. July 1997. The incidence of acardia which was found in this material is more than three times higher than the incidence generally given in the literature. Presenting the cases, the contemporary possibilities of prenatal diagnosis of this highly pathologic form of monozygotic twin pregnancy are discussed in details, further a survey is given of the new, so far experimental, but promising, less and less invasive interventions directed towards in utero terapy by closing the connecting vessels, including also laser occlusion of chorioangiopagus.