Long-term clinical performance of mitral tissue valves was analyzed in a consecutive series of 250 patients (131 men, 118 women; mean age 51 years) over a 13-year period. Mean follow-up was 71 months (range 1-141 months). The total cumulative follow-up period was 1466 years. The late mortality was 2.0% per patient-year, whereas thromboembolism occurred in 1.4% per patient-year, prosthetic valve endocarditis in 1.0% per patient-year, periprosthetic leaks in 0.3% per patient-year and structural valve deterioration in 3.0% per patient-year. The rate of reoperation was 3.4% per patient-year. Actuarial analysis showed the following results (1 year/5 years/10 years): Survival rate: 97 +/- 1%/89 +/- 2%/82 +/- 5%; free of embolisms: 98 +/- 1%/96 +/- 1%/86 +/- 5%; free of endocarditis: 99 +/- 1%/95 +/- 2%/90 +/- 3%; free of valve deterioration: 99 +/- 1%/96 +/- 1%/60 +/- 8%; no reoperation: 98 +/- 1%/94 +/- 2%/57 +/- 8%; free of late complications: 92 +/- 2%/77 +/- 4%/41 +/- 10%. On the basis of our statistical evaluation the probabilities are that, 11 years after implantation of a mitral bioprosthesis: (a) only 35% of patients are free of late complications (including thromboembolisms, prosthetic valve endocarditis, structural valve deterioration and death); (b) and only 50% of patients have not needed reoperation.