The principal feature of bioprosthetic valve which remains to be completely defined is long-term durability, especially, with regard to the impact of patient age. This report provides extended data regarding valve durability derived from a data base of 515 patients who received lonescu-Shiley bioprosthetic valve between 1978 and 1985; cumulative duration of follow-up was 1562.3 patient-years, with a maximum follow-up duration of 8.7 years. The results of this survey showed as follows: 1] The actuarial freedom from valve failure at 6 years were 43*7% for 0-19 year-old group, 70*1% for 20-39 year-old group and 75*1% for over 40 year-old group separately. 2] Of the causes of valve failure, only the primary tissue failure was markedly influenced by patient`s age [p<0.001], but the prosthetic valve endocarditis was not [p>0.1]. 3] The linealized incidences of primary tissue failure were 7.31% per patient-year in 0-19 year-old group and 0.12% in 20-39 year-old group. 4] The primary tissue failure rate in 0-19 year-old group was 6.36% during first 4 years, but then increased upto 10.95% at postoperative 5 year. Thus we find that in bioprosthetic valve the primary tissue failure is apt to occur when patient is young [especially less than 20 years old] and the postreplacement time passes [especially over 5 years]. The rate of bioprosthesis failure among children and adolescents is clearly higher than that observed in adult patients; however, conclusive quantification of time-related risk for young patient is not yet possible on the basis of existing data. Therefore, the advisability of bioprosthesis implantation in children remains to be determined.