PURPOSE: Single umbilical artery (SUA), the most common malformation of the umbilical cord, has long been of interest because of its association with congenital malformations. This retrospective study was aimed to evaluate the incidence of SUA and its associated malformations. METHOD: The study population was inborn neonates of Kang-Nam Sacred Heart Hospital of Hallym University. We reviewed retrospectively the medical records of 15 infants with SUA, including 1 infant identified in prenatal ultrasonography. RESULTS: The incidence of SUA was 0.2% (15/9,351 cases). The mean birth weight was 2,658 gram (ranged from 1,060 to 3,700gram), and the mean gestational age was 38 weeks (ranged from 32 to 40 + 3weeks). Six cases (40%) of 15 cases with SUA were associated with congenital malformations : urogenital malformations in 4 cases, cardiovascular malformations in 3 cases, and musculoskeletal malformations in 3 cases. Only 1 case had abmormal karyotype, trisomy 18. CONCLUSION: Because SUA is highly associated with congenital malformations newborns with SUA should have a thorough and complete physical examination at birth and physicians should also be alert to the possibility of congenital malformations not evident at initial examination. Furthermore, prenatal detection of SUA has potential importance, since it may indicate that further work is necessary to rule out associated malformations and to help determine whether management should beltered.