An unusual venous anomaly of the placenta. The authors present an unusual vascular anomaly of the placenta. The placenta was very large, weighing 1,490 g. On the fetal surface, numerous dilated and tortuous vessels were observed on and under the chorionic membrane, of which three branches arose from a vein that was connected to the umbilical vein. One of them had a 5 x 2.5 cm aneurysmal dilatation, where three secondary branches arose. These venous channels were dilated and tortuous. The longest secondary branch was 133 cm in length and 1.2 cm in mean diameter and led into the placenta. Multiple, severely coiled or straight small branches arising from these vessels were also observed as vascular tangles. Some of these smaller vessels also led into the placenta. All abnormal vessels were veins. The umbilical cord was also normal except for a membranous insertion, and the placenta was unremarkable except for its large size. 