From 1976 to 1989, 122 patients underwent isolated mitral valve replacement with a bioprosthesis for non-ischaemic mitral insufficiency. There were 76 women and 46 men, with a mean age of 52 years. Mitral valve disease was of rheumatic origin in 71 (58%), due to myxomatous degeneration in 50 (41%), and congenital in one. Early mortality was 3.3% (4 pts). The 10-year survival was 65 +/- 7%. A follow-up was available for all 122 patients, averaging 78 months, for a total of 763 patient-years. Valve-related (VR) complications included: 16 thromboembolic episodes in 13 patients (2.1% pt-yr), 3 endocarditis in 2 patients (0.4% pt-yr), and 20 reoperations (2.6% pt-yr), 19 of which were due to intrinsic structural deterioration of the tissue valve. There was no haemorrhagic episode. Overall, 32 patients suffered a VR complication (4.2% pt-yr). The 10-year freedom rates from haemorrhage, endocarditis, thromboembolism, and reoperation were 100%, 98%, 87%, and 64% respectively. After 10 years, 87% of the patients were free from VR mortality, 84% were free from VR mortality and permanent disability, and 52% remained free from all VR complications. While 69% of the patients (84 pts) were in functional class III or IV preoperatively, 89% (102 pts) of the survivors were in class I or II after operation. Excellent survival and clinical results have been obtained with the use of bioprostheses in this disease. However, because durability beyond 10 years appears to be limited and the cause of major morbidity, tissue valves are now used more selectively.