We report two children with typical Williams syndrome facial appearance, growth deficiency and developmental delay. Both had supravalvular aortic stenosis (SVAS) and peripheral pulmonary stenosis (PPS), but no hypercalcemia. Chromosomal study in the first case, a 40-day-old girl, revealed a cytogenetically visible proximal interstitial deletion of the 7q11.22-11.23 segment. Another patient, a 3-year-old boy, with a normal karyotype, had milder phenotype with spontaneous remission of SVAS and PPS. Both patients showed allelic loss of the elastin (ELN) gene, exhibiting a submicroscopic deletion at 7q11.23, which was detected by fluorescence in situ hybridization (FISH). The results support the usefulness of FISH for detection of ELN gene deletion as an initial diagnostic assay for patients with SVAS or Williams syndrome. To our knowledge, these are the first cases of Williams syndrome in Taiwanese patients to be proven clinically, cytogenetically and by molecular analysis.