Valve replacement still represents a problem in the very young patient. Between July 1988 and November 1993, 96 CarboMedics mechanical valves were implanted in 75 patients with a mean age of 11.76 years (range, 5 months to 20 years). The mean preoperative New York Heart Association functional class was 3.2, and 89.3% of the patients were in sinus rhythm. The cause was rheumatic in 60%, congenital in 24%, and infective in 12%. Mitral valve replacement was undertaken in 43 patients, aortic in 11, and mitroaortic in 21. Among the 18 patients with congenital defects, 13 required simultaneous repair of their complex lesions. The hospital mortality was 12% (9 patients). Cause and age were significant factors responsible for mortality. The mortality was 27.8% for patients with congenital disease and 6.7% for those with rheumatic defects (p = 0.0365); it was 40% for patients younger than 2 years, 14.3% for those between 3 and 10 years old, and 5.9% for those older than 10 years (p = 0.0108). The maximum follow-up was 54 months (mean, 18 months). There were 10 late deaths (15.15%). No embolic events occurred. All patients were on anticoagulation therapy except 2 who were on antiaggregant therapy. One of them underwent successful reoperation for treatment of mitral prosthetic thrombosis. Three reoperations were performed: one for thrombosis, one for perivalvular leak, and one for endocarditis. The total actuarial survival was 68.19% +/- 7.02%. Freedom from embolism was 100%; from thrombosis, 96.72% +/- 3.22%; from severe hemorrhage, 94.94% +/- 3.67%, and from reoperation, 83.07% +/- 9.51%.