From April 1990 to May 1994, 89 patients (median age, 42 years; range, 10 days to 66 years) underwent aortic valve or root replacement with allografts or autografts. Thirteen patients were less than 18 years old at the time of operation. Indication for aortic valve replacement was aortic stenosis (50 patients, 56%), small stenotic prosthesis (2 patients, 2%), aortic valve endocarditis (19 patients, 21%), isolated aortic regurgitation (17 patients, 19%), and type II truncus arteriosus (1 patient, 1%). The subcoronary implantation was used in 45 patients (group A), and implantation of an intraluminal cylinder (16 patients) or complete root replacement (28 patients) was performed in the remaining 44 patients (group B). The Ross procedure was performed in 22 patients. Intraoperative transesophageal echocardiography was used routinely. Five patients died in the early postoperative period (6%), 2 in group A and 3 in group B. Three other patients required immediate replacement of a failing graft by a mechanical prosthesis (1 in group A and 2 in group B). There has been no late death. All survivors remained in New York Heart Association functional class I and were free of thromboembolic complications. Endocarditis occurred in 2 patients, 1 year after operation. Both were successfully treated medically. Echocardiographic studies were obtained serially in every patient. Four patients, 2 in group A and 2 in group B underwent reoperation because of mild-to-moderate aortic regurgitation (rate of reoperation, 5%). Two valves were repaired and two were replaced by an allograft.(ABSTRACT TRUNCATED AT 250 WORDS)