Registry data on all infants born in Sweden between 1983 and 1986 are reviewed to describe perinatal mortality and malformation rate of infants with single umbilical artery (SUA). Since SUA is much more common in infants with chromosomal anomalies and in twins this analysis is confined to the 1694 singletons who were not recorded as having chromosomal anomalies. There was significantly increased risk of perinatal mortality among these infants largely due to an increased frequency of congenital malformations, low birthweight and preterm delivery. Nevertheless, at least 36% of the perinatal mortality occurred in the absence of malformations or low birthweight. We found the overall risk of severe malformation in SUA infants to be increased 4.3 times. Some malformations were especially common, such an anorectal atresia and oesophageal atresia.