Aneurysm of the umbilical vessels is a rare abnormality and has seldom been diagnosed prenatally. We report a case in which dilatation of the intra-amniotic umbilical cord was seen on prenatal ultrasound at 34-weeks gestation. This was believed to represent an umbilical vein aneurysm and was confirmed on subsequent pathological examination after delivery. A review of the literature concerning these uncommon vascular abnormalities of the umbilical cord is presented.