Between July 1970 and June 1977, 151 patients underwent isolated mitral valve replacement with the Björk-Shiley valve. The follow-up period extended over 8 years to June 1978. Hospital mortality was 5.2% (8/151), late mortality 8.4% (12/143). Actuarial survival analysis predicts 84 (± 4)% of patients to be alive at 5 years and 80 (± 6) % at 8 years. Thirteen patients sustained 15 episodes of thromboembolic complications; actuarially 88 (± 4) % of patients were free from this complication at 5 years and 81 (± 8) % at 8 years. Other valverelated complications included paravalvular leak (7), prosthetic endocarditis (4), and disc dislodgement (1). Postoperative clinical classification showed an improvement of at least one class in 84 % of patients.