Replacement of cardiac valves in childhood is infrequent primarily because of the rarity of anatomical lesions requiring valve replacement. Furthermore, there are uncertainties regarding the long-term fate of the prosthetic valve and the effects of a fixed-orifice valve in the growing child. In 15 children, 15 years old or younger, a cardiac valve was replaced because of congenital or acquired valvar heart disease. There were eight mitral valves, five aortic valves, and three tricuspid valves replaced. Indications for replacement were uncontrollable congestive heart failure or an apparently fatal course. Initial mortality was 25% with an additional 12.5% late deaths. Complications including embolization, mechanical "ball-valve failure," arrhythmias, hemolytic anemia, and difficulties with anticoagulants were not peculiar to childhood. Postoperative improvement was dramatic. Replacement should be considered before irreversible changes occur that preclude a satisfactory outcome.