Evaluation of 19 patients with the Williams elfin facies syndrome, in order to more completely delineate the total spectrum of the disorder, indicates that "infantile hypercalcemia, peculiar facies, supravalvular aortic stenosis" designation which was heretofore used is inappropriate. Only 32% of the patients have evidence of supravalvular aortic stenosis and not one of them has had documented hypercalcemia, including eight patients who had a serum calcium determination in the first year of life. Rather, the most consistent features are growth deficiency which is predominantly of postnatal onset, mild microcephaly with mental deficiency, and an altered pattern of facial development which includes short palpebral fissures, a stellate pattern in the iris, medial eyebrow flare, a depressed nasal bridge with anteverted nares, and thick lips. The disorder is a sporadic occurrence of unknown etiology.