Ductus venosus links the umbilical vein and the portal vein to the inferior vena cava. It is of great significance for the developing fetus but of minor importance to the growing infant where it normally obliterates and is transformed to the ligamentum venosum. An absent ductus venosus implies that the oxygenated blood from the umbilical vein has to circulate through the liver. We report 4 cases with this malformation. Prenatally, three fetuses had an extreme hydrops, especially hydrothorax. In two fetuses hydrops was severe already in the second trimester of pregnancy. Termination was performed. In the third case, hydrops was first diagnosed in the 36th week of gestation. The fourth case had an ultrasound examination in the 34th week of gestation. There was no hydrops but a disproportion with a very small head and abdominal diameter compared to femur length. Postpartum both these infants died. At autopsy, the only structural malformation in the three hydrops cases was an absent ductus venosus. In the fourth case there were other anomalies.