Pre- and postnatal growth retardation of unknown pathogenesis is a common clinical feature in patients with Williams-Beuren syndrome (WBS). However, growth hormone deficiency (GHD) has not been considered a major cause of growth retardation. There is only one patient in the literature with confirmed GHD who responded well to human growth hormone (hGH) therapy. We report a female infant with confirmed WBS who, through provocative testing, was found to have GHD and who responded satisfactorily to hGH therapy. Height SDS was -4.2 at the age of 12 months when hGH was initiated and increased to -0.8 at the age of 4.25 years. The pathogenesis of GHD in our patient is unclear. Nevertheless, the elevated levels of prolactin and the response of hGH to growth hormone releasing hormone (GHRH) administration are indicative of a hypothalamic rather than pituitary defect. In conclusion, GH deficiency might contribute to the growth failure in a number of patients with WBS and in such cases hGH therapy will most likely improve final height.