Objective: To evaluate the relationship of single umbilical artery with congenital anomaly, chromosmal anomaly & pregnancy outcome. Methods: From January 1993 to December 2000, 143 cases of single umbilical artery were observed among 72,194 total deliveries at Ilsin christian hospital. Pregnancy and perinatal outcome data were retrieved by review of the medical records. Results: The incidence of single umbilical artery (SUA) was 0.2% (143 cases). Isolated SUA without any anomaly were 89 cases (62.2%), SUA with anomaly were 42 cases (29.4%); with multiple anomaly were 20 (14%) and stillbirth were 12 (8.4%). Cardiovascular & musculoskeletal system anomalies were common congenital anomalies, 35.7% respectively. Among the 86 cases (60.1%) of chromosomal studies, chromosomal anomalies were observed in 4 cases (2.8%); 2 cases were Trisomy 18, 2 cases were 45,XX,-13,-14,+t (13q:14q), 46,XY,t(1:9) (q11:q11). No chromosomal anomaly was observed in isolated SUA without any other anomaly. On 74cases with obstetric complication, intrauterine growth restriction (n=27, 20.6%), preterm birth (n 12, 10%), hydramnios (n=11, 8.4%), oligohydramnios (n=7, 5.3%), preeclampsia (n=6, 4.6%), maternal gestational DM (n=5, 3.8%) were observed. Conclusion: When a single umbilical artery is identified during antenatal care, careful search such as targeted ultrasonography & fetal echocardiography should be taken for associated anomaly, and chromosomal study should be considered in case of SUA with any anomaly.