Williams- Beuren syndrome (WBS) is a segmental aneusomy syndrome that results from a heterozygous deletion of contiguous genes at 7q11.23. WBS is a rare neurodevelopmental disorder with phenotypical variability. WBS is characterized by distinct facial changes, hyperacusis, mental retardation and congenital heart defect (particularly supravalvular aortic stenosis (SVAS). While WBS is the result of deletion of ELN, LIMK1 and 21 contiguous genes, point mutations within the elastin gene result in autosomal dominant disorders - supravalvular aortic stenosis. A pilot study has been carried out to assess the reliability of the detection of deletion at the elastin locus by conventional chromosome analysis and fluorescence in situ hybridisation (FISH) analysis as diagnostic tests in classical, suspected and atypical WBS patients with SVAS. MATERIALS AND METHODS: We report clinical evaluation, cytogenetics analysis, FISH-investigations were held for 23 patients referred to test for WBS. For FISH- analysis we used LSI Williams Region (DNA Probe ELN, LIMK SO/D7S486.D7S522SG (VYSIS). RESULT: From 23 cases studied by FISH, 18 showed the microdeletion of the critical region. No deletion was demonstrated in another 3 patients in whom an earlier clinical diagnosis of WBS was judged doubtful and 2 patients with isolated SVAS. Conclusions: The FISH analysis is very informative for diagnostic values. Children with developmental retardation and WBS dysmorphic signs and with SVAS/PS heart defect should be examined by a cytogenetic and molecular cytogenetic FISH analysis. This study confirms the usefulness of genetic studies as a diagnostic tool for Williams - Beuren syndrome.