Williams syndrome (WS) is a well- recognized neurodevelopmental disorder man ifested by both connective tissue and CNS abnormalities. The study depicts the 8 - y experience and follow- up of 50 Greek children with the clinical diagnosis of WS. Clinical data on the facial features and cardiovascular, endocrinologic, and neurodevelopmental evaluation are presented. The most consistent findings w ere dysmorphic features (100% ), followed by dental anomalies (90% ) and hyper acousis (90% ). Only eight of 50 children had severe cardiovascular defects tha t required surgical intervention during the first year of life. Supravalvular ao rtic stenosis was less frequent (28% ) than shown in the literature. Severe hyp ertension was noticed in 22% of our patients, and infantile hypercalcemia was noticed in 6% . Twelve percent of our patients showed an elevation of CPK. Most children presented with moderate to severe mental retardation with IQ ranging f rom 20 to 85. Elastin hemizygosity was detected by fluorescence in situ hybridiz ation. Dinucleotide repeat polymorphism analysis was performed in an attempt to correlate phenotype with genotype. The origin of deletions was more frequently m aternal (59% ), and a more severe phenotype seemed to be associated with those deletions. This is the first report on WS patients in the Greek population. Williams study (WS) is a well-recognized neurodevelopmental disorder man ifested by both connective tissue and CNS abnormalities. The study depicts the 8-y experience and follow-up of 50 Greek children with the clinical diagnosis of WS. Clinical data on the facial features and cardiovascular, endocrinologic, and neurodevelopmental evaluation was presented. The most consistent findings w ere dysmorphic features (100%), followed by dental anomalies (90%) and hyper acousis tha t required surgical intervention during the first year of life. Supravalvular ao rtic stenosis was less frequent (28%) than shown in the literature. Severe hyp ertension was noticed in 22% of our patients, and infantile hypercalcemia was noticed in 6%. Twelve percent of our patients showed an elevation of CPK. Most children presented with moderate to severe mental retardation with IQ ranging fom 20 to 85. Elastin hemizygosity was detect ed by fluorescence in situ hybridiztion. Dinucleotide repeat polymorphism analysis was performed in an attempt to correlate phenotype with genotype. The origin of deletions was more frequent m aternal (59%), and a more severe phenotype was be associated with those deletions. This is the first report on WS patients in the Greek population.