BACKGROUND Long-term survival for combined aortic and mitral valve replacement appears to be determined by the mitral valve prosthesis from our previous studies. This 21-year retrospective study assess long-term outcome and durability of aortic valve replacement (AVR) with either concomitant mitral valve replacement (MVR) or mitral valve repair (MVrep). We consider only a single mechanical prosthesis. METHODS Three hundred and sixteen patients underwent double valve replacement (DVR) (n = 273) or AVR+MVrep (n = 43), in the period 1977 to 1997. Follow up of 100% was achieved via telephone questionnaire and review of patients' medical records. Actuarial analysis of long-term survival was determined by Kaplan-Meier method. The Cox regression model was used to evaluate potential predictors of mortality. RESULTS There were seventeen cases (5.4%) of early mortality and ninety-six cases of late mortality. Fifteen-year survival was similar in both groups at 44% and 57% for DVR and AVR+MVrep respectively. There were no significant differences in valve related deaths, anticoagulation related complications, or prosthetic valve endocarditis between the groups. There were 6 cases of periprosthetic leak in the DVR group. Sex, pre-operative mitral and aortic valve pathology or previous cardiac surgery did not significantly affect outcome. CONCLUSIONS The mitral valve appears to be the determinant of survival following double valve surgery and survival is not significantly influenced by mitral valve repair.