In a girl with Williams-Beuren's syndrome psychological examination revealed mental retardation with a special mental profile, angiography revealed peripheral pulmonary stenoses, echocardiography a slight stenosis in the supravalvular aortal area and anthropometry typical facial signs. Indirect signs of hypercalcaemia were clinical signs of poor progress during infancy. The authors emphasize that accurate analysis of basic clinical signs and the natural development of the disease are the key to its diagnosis.