From 1980 to 1996, 111 patients (83 females, 28 males, mean age 51.47 +/- 15.73 years, range 1-76) underwent mitral valve replacement. Seventy-five patients underwent replacement of a biological valve and 36 of a mechanical valve. Three patients underwent a third operation. Seventy prostheses were replaced because of a structural dysfunction. Other causes of valve failure were: 24 thrombosis (23 mechanical and 1 biological), 10 endocarditis (7 mechanical, 3 biological) and 4 leakages (3 mechanical and 1 biological). One patient who had recurrent anticoagulant-related haemorrhage underwent reoperation to replace his mechanical valve with a biological prosthesis. Two patients had their valve replaced because of mismatch between size of the valve and body surface area. Thirteen operations were performed on emergency and 29 on urgency. There were 22 in-hospital deaths with a hospital mortality of 19.82%. Fourteen deaths (63.63%) occurred in patients operated on emergency or urgency. All deceased patients were in NYHA functional class III or IV. Our data suggest that risk of reoperation on mitral prosthesis is highly influenced by the preoperative functional class. In spite of the fact that replacement of biological valves should be more elective than that of mechanical valves, we did not find any difference between the two groups of patients.