Two brothers with Williams syndrome without hypercalcaemia are presented. One boy died during the first month of life. His brother also had the typical phenotypic features of the elfin fades. He developed severe microcephaly and cataract and died at the age of 9 years. The skeleton was osteosclerotic at birth, and became generally osteoporotic at the age of 2 years. He had persistently elevated 1,25-dihydroxyvitamin D levels during the first 2 years of life, in spite of normocalcaemia. At autopsy, microcalcifications were found in the brain and kidneys. The present report underscores the familial occurrence of Williams syndrome of severe degree. Elevated 1, 25-dihydroxyvitamin D levels without hypercalcaemia have not been reported previously, and may suggest causal heterogeneity of the Williams syndrome.