Williams syndrome has been variably termed Williams–Beuren syndrome, idiopathic hypercalcemia, and supravalvar aortic stenosis syndrome. It is estimated to occur in 1/10,000 births. The clinical diagnosis of Williams syndrome is based on the recognition of the characteristic pattern of dysmorphic facial features, developmental delay, short stature relative to the family background, connective tissue abnormality, unique cognitive profile, and typical personality, which includes overfriendliness, empathy, distractability, and anxiety. This disorder is caused by a submicroscopic deletion of chromosome 7q11.23 that arises by an unequal crossing over in a chromosome region where there are a large number of repetitive DNA sequences. The commonly deleted region is approximately 1.5 Mb, and 26 genes have thus far been mapped within it. Many of the medical manifestations of Williams syndrome are caused by deletion of the elastin gene. Management is informed by knowledge of the natural history and manifestations of the condition.