This study examines the developmental history of 32 Williams syndrome patients, positive to the fluorescence in situ hybridization (FISH) test. The information is intended to provide help for early diagnosis and appropriate stimulation of these patients. In the sample reported here, only about half of the patients referred with presumptive diagnosis were in fact FISH+, indicating that facial dysmorphism may not be the most reliable sign for diagnosis. Initial pediatric signs are developmental delay and nocturnal irritability. In consultation, facial dysmorphies and heart murmur are detected. There is also low birth weight, failure to thrive, unsuccessful breastfeeding, and gastroesophageal reflux. All these symptoms are strongly suggestive of Williams syndrome. Subsequent steps consist of cardiologic studies. Our results indicate that the triad of symptoms consisting of infantile hypercalcemia, dysmorphic facies, and supravalvular aortic stenosis, which until recently was considered fundamental for Williams syndrome diagnosis, is not usually present and does not lead to an early diagnosis. Cognitively, these children are characterized by hypersociability, hyperacusia, deficient visuoconstructive abilities, attentional deficit and hyperactivity, and in some cases, spontaneous musical interests. There are no special verbal skills. The results of this study indicate that the concept of Williams syndrome patients as language- and musically-gifted is not fully accurate.