The Fragile-X Syndrome (FXS) is a disorder linked to X chromosome, on the long arm Xq27.3, causing several changes such as behavioral problems, intellectual disability, macroorchidism, large and prominent auricles, deep and ogival palate, mandibular prognathism, increased mandibular angle, malocclusion, and dental anomalies. The objective was to present a case of a 16-year-old patient with FXS, leukoderma, submitted to orthopedic functional maxillary treatment to correct dental crowding. In general, clinical examination, behavioral changes such as shyness, anxiety, emotional lability, sporadic disturbances of behavior associated with mild mental disabilities were remarkable. After panoramic radiographic evaluation and cephalometric tracings, it was decided to install the functional orthopedic appliance of the jaws, Indirect Flat Planes type, for later corrective orthodontic treatment. At...