We have reviewed the natural history of congenital ulnar deficiency in 15 limbs in our series and in 185 limbs in the literature. The natural history suggests that there is little progression of deformity. Specific variables for prognosis have not been determined. There are no data that discuss relative ulnar length or relative forearm shortening of the involved extremity. We compared function in our 15 limbs with standards of function in the general population. Based on our findings, treatment must be individualized to maximize function and should be conservative regarding ulnar deviation of the wrist, radial head dislocation, and preservation of forearm pronation and supination. Standard reconstruction of hand anomalies is most rewarding for functional results.