Background Cardiovascular manifestations are known to be common in Williams syndrome (WS). We report the fate of semilunar supravalvar stenosis of WS in a tertiary center. Methods We reviewed the medical records of patients who were diagnosed as WS between 1985 and 2015 at the Seoul National University Children’s Hospital. Results One hundred two patients were diagnosed as WS between 1985 and 2015. Among them, 59 were male and 43 were female. The mean age at diagnosis was 29.4 months. Among 98 patients who had initial echocardiography (echoCG) records, only 5(5.1%) patients had no cardiovascular (CV) manifestation. Supravalvar aortic stenosis (SVAS) (81 patients; 82.7%) was the most common CV manifestation and supravalvar pulmonary stenosis (SVPS) (47 patients; 48.0%) was followed. Among 102 WS patients, 25 patients (24.5%) underwent cardiovascular operation. The mean age at operation was 74.2 months. Aortoplasty (18 patients, 72%) was the most common operation. In the patients with aortoplasty, the peak velocity of SVAS and z-score of sinotubular junction (STJ) of aorta at surgery was 4.31m/s and -4.34, respectively. Latest echoCG in these patients showed that peak velocity of SVAS was 1.86m/s and z-score of STJ of aorta was -0.15. Of 77 WS patients who were not underwent operation, 57 patients had initial and latest echoCG records. There was a trend of reliving SVAS and SVPS in those patients. SVAS was relived spontaneously in 12 of 49 patients who had SVAS initially. Furthermore mean STJ z-score of aorta of 37 patients who still had SVAS were increased. In SVPS, this trend was more prominent. Of 32 patients who had SVPS initially, 17 patients improved spontaneously. And 15 patients who still had SVPS, their peak velocity of SVPS was decreased without treatment. Conclusion CV manifestation was more frequent in WS than we thought. SVAS is most common CV manifestation in WS. The natural course of CV manifestation of WS would be quite optimistic. However, a quarter of them needed surgery due to SVAS. Thus, the patients with WS require regular follow-up until adulthood.