Thumb hypoplasia, congenital underdevelopment of the thumb, can range from a slight decrease in thumb size to complete absence of the thumb. As part of the radial longitudinal deficiency spectrum, other organ systems may be affected as well. Hence, the global health of the child should be addressed before focusing on the thumb. The decision of whether to reconstruct the existing thumb or to ablate the thumb and perform a pollicization of the index finger hinges primarily on the examination of trapeziometacarpal joint stability. Ultrasound imaging may play a role in decision making in borderline cases. The ultimate goal of surgical treatment is to provide a stable and functional thumb.