Mandibular symphyseal distraction osteogenesis has recently been introduced as a means of resolving arch length deficiencies in the anterior segment and as a method of reducing large vestibular spaces related to a narrow mandible. Accurately relating the required distraction for a given anterior tooth mass and desired future anteroposterior location of the central incisors has not been possible until recently. The relationship between these 3 controlling factors has been mathematically described by the hyperbolic cosine function and a computer program designed for easy use by the clinician. Two clinical cases illustrate the application of the program. A Web site where the program can be downloaded at no cost is mentioned.