Valve replacement in children has always been associated with a high mortality, outgrowth of the prosthetic valve and difficulty in managing anticoagulation. Between January 1985 and April 1991, 20 patients (14 males and 6 females) underwent replacement of a left-sided cardiac valve. The median age at diagnosis was 21.6 months (1 to 120 months) and the median age at surgery was 85 months (11 to 213 months). Six patients were under 4 years of age. The site of valve replacement was aortic in 11 patients and left atrioventricular (AV) valve in 9 patients. The indications for aortic valve replacement were stenosis (6) and incompetence (5). The left AV valve was replaced in three patients following repair of AV septal defect, in one patient with corrected transposition of the great arteries (LTGA), in one patient with severe dysplasia and insufficiency, and in four patients for congenital mitral stenosis. A Bjork-Shiley prosthesis was used in three mitral and one aortic position, all the other patients receiving a St. Jude prosthesis: six mitral and ten aortic. All patients were anticoagulated (warfarin) for 3 months post implantation and then switched to a regimen of aspirin and persantine. There was no early or late death. Median follow-up was 12.3 months (4 to 72 months). Total follow-up was 59 patient-years or 708 months. There was one incident of thromboembolism (1.7%/patient-year) and four instances of bleeding (6.8%/patient-year). There was no valve thrombosis. Our regime of early warfarin followed by long-term antiplatelet therapy has been associated with a low incidence of thromboembolism and no valve thrombosis.