Abstract OBJECTIVES Our aim was to analyse outcomes after implantation of mechanical versus biological valve prostheses in patients presenting with left-sided infective endocarditis. METHODS We conducted a retrospective single-centre cohort study, analysing adults requiring valve surgery for left-sided infective endocarditis between January 2009 and December 2018 at the Department of Cardiac Surgery, Medical University of Vienna. The primary outcome variable was all-cause mortality. Secondary outcome variables included the occurrence of a combined event (death, stroke, intracerebral bleeding or reoperation) and the risk of re-endocarditis. RESULTS Among 220 patients, 76 (34.5%) underwent mechanical valve replacement, while 144 (65.5%) underwent biological valve replacement. Recipients of mechanical valve prostheses were younger at the time of surgery and presented with lower European System for Cardiac Operative Risk Evaluation II values. In patients <55 years of age, implantation of a mechanical valve prosthesis was independently associated with significantly lower risk of all-cause mortality (adjusted hazard ratio 0.35, 95% confidence interval 0.15–0.80, P = 0.013). Moreover, this group was at significantly lower risk of a combined event (adjusted hazard ratio 0.38, 95% confidence interval 0.19–0.76, P = 0.006). Implantation of a mechanical valve prosthesis was not associated with increased risk of re-endocarditis. The presence of an annular abscess significantly increased the risk of re-endocarditis (adjusted hazard ratio 3.06, 95% confidence interval 1.40–6.71, P = 0.005). CONCLUSIONS In patients presenting with left-sided infective endocarditis <55 years of age, implantation of a mechanical valve prosthesis is associated with superior outcomes. A prospective randomized controlled trial is warranted to confirm these results.