Risk factors of operative mortality and long term survival were identified in 219 patients who underwent mitral valve replacement (MVR) using Bjørk-Shiley mechanical prostheses. Early mortality was 7.3%. The accumulated follow-up time was 1134 patient-years, and the 5-year survival for the total cohort was 78 +/- 3%. Independent prognostic factors of early mortality were poor NYHA class, which carried a relative risk (RR) of 3.2, and ischaemic aetiology, with a RR of 2.2. Ischaemic aetiology was the sole predictor of heart pump failure requiring intra-aortic balloon pump support (RR = 2.7). Independent risk factors of total mortality (early and late) were male sex (RR = 2.3), NYHA class III-IV (RR = 2.4), presence of mitral regurgitation (RR = 3.2) and relative heart volume (RR = 1.6 for a 800 ml/m2 size compared to a heart of 550 ml/m2). Our results underline the importance of patient-related factors in MVR, and indicate that care is needed in comparing the quality of MVR from different institutions with respect to mortality and morbidity. The results of MVR are palliative rather than curative except in female patients with NYHA class II function and mitral stenosis, in whom cure was attained.