Williams syndrome, also known as Williams-Beuren syndrome, or elfin-facies syndrome, was described by Dr. Williams and Dr. Beuren for the first time in 1961 and 1962. This multisystem, congenital and panethnic disorder is characterized by a number of developmental and physical abnormalities like excess of gingiva. The goal of this article is to present the application of a protocol of periodontal treatment leading to the functional rehabilitation of the oral areas affected by excess of gingiva. A 19-year-old boy, diagnosed as suffering from Williams Syndrome, was brought to the dental school, University of Cagliari, seeking for orthodontic and periodontal treatment. During the consultation the excess of gingiva needing periodontal treatment was noticed. This report reveals a classic presentation of the syndrome, with emphasis on its oral and periodontal manifestations. Periodontal management included periodontal flap surgery to treat the excess of gingiva performing clinical crown lengthening. Re-evaluation of the patient after two months showed remarkable reduction of the excess of gingiva. Williams syndrome is clinically important to the periodontist, because of its associated features of excess of gingiva. Periodic examinations are recommended to identify any possible recurrence or complications.