Williams syndrome is a multifaceted disorder that includes a spectrum of cardiovascular anomalies. Due to its rare occurrence, outcome data for operations and cardiac catheterization are limited. We reviewed data from 242 individuals from the Pediatric Cardiac Care Consortium (PCCC) with Williams syndrome and associated cardiovascular lesions, and their frequency, and assessed their effects on mortality. In the PCCC, from 1984 to 1999 there were approximately 100,000 entries for cardiac procedures, involving more than 62,000 patients. The diagnosis of Williams syndrome was based on clinical features and determined by each site. Most patients were diagnosed with the availability of the FISH probe for region 7q11.23. Using a spreadsheet application, Microsoft Excel, the selected patients were analyzed for various types of cardiac anomalies. The most common cardiovascular lesions and the mortality rate in patients with Williams syndrome were examined. A complete tabulation of all cardiovascular lesions was assembled. There were 292 catheterizations and 143 operations reported to the PCCC. One hundred six patients had both an operation and a catheterization. The three main cardiovascular anomalies were supravalvular aortic stenosis (SVAS; 169), pulmonary artery stenosis (PAS; 130), and coarctation or aortic arch hypoplasia (Arch; 32). One hundred five patients had a single lesion, 70 with SVAS, 29 with PAS, and 6 with an arch anomaly. Ninety-two had more than one lesion: 80 with SVAS and PAS, 7 with PAS and Arch, and 5 with SVAS and Arch. Seventy individuals have only SVAS, 29 PAS, and 6 Arch alone. There was a total of 15 deaths. The mortality rate was highest in the group with the combination of SVAS and PAS (7 surgical and 5 catheter; 12 of 80 patients [15%]; p = 0.0001, χ²). In conclusion, our data represent the largest collection of individuals with Williams syndrome who underwent cardiac catheterization and/or operation. The data suggest that children with Williams syndrome and bilateral outflow tract obstruction have statistically and clinically significantly higher mortality associated with catheterization or operation.