Williams syndrome is a rare congenital disorder with various physical abnormalities and characterized by facial, oral, and dental features. Individuals with Williams syndrome typically have eating disorders in the early childhood, which lead to prolonged night feeding. Prolonged night feeding is a risk factor for rampant dental caries. Williams syndrome is caused by the microdeletion of chromosome 7, resulting in elastin deficiency. Elastin is integral to cardiovascular health. Many patients with Williams syndrome have complex cardiovascular abnormalities that must be considered a part of dental management. Complications related to cardiovascular diseases may induce adverse effects such as dangerously elevated blood pressure. This may occur in patients during stressful dental treatment. In addition, characteristics of auditory hyperalgesia and anxiety disorders among patients with William syndrome, complicate receiving routine dental management. Therefore, dental treatment under sedation or general anesthesia may be preferable for patients with Williams syndrome; in particular, patients who are very uncooperative and/or needs extensive dental treatment. A thorough evaluation of each patient's physical condition is required before making decisions regarding dental treatment. Careful monitoring and preparation for emergencies are very important during and shortly after dental treatment under general anesthesia or sedation. Monitoring is critical until vital signs have stabilized and return to normal. A 28-month-old man diagnosed as having Williams syndrome, visited the Dental Hospital of OO University for the management of rampant dental caries. We reported on the management of this patient who had peripheral pulmonic stenosis, and received dental treatment under general anesthesia. We also reviewed the characteristics of Williams syndrome and discussed considerations for dental treatment under general anesthesia.