OBJECTIVE: Patient-prosthesis mismatch (PPM) has been reported to increase perioperative mortality and reduce postoperative survival in patients undergoing aortic valve replacement (AVR). We analysed the effect of PPM at values predicting severe mismatch on survival following AVR in our unit. METHODS: Prospectively collected data on 1481 consecutive patients who had undergone AVR with or without coronary artery revascularisation between 1997 and 2005 were analysed. Projected in vitro valve effective orifice area (EOA) and geometric prosthesis internal orifice area (GOA) were evaluated and values were indexed to body surface area (cm(2)m(-2)). PPM was defined as EOAi80, RR 2.13, 95% CI 1.38-4.586, p=0.004). CONCLUSIONS: Severe patient-prosthesis mismatch was predicted in 4-10% of patients undergoing AVR but this did not affect in-hospital mortality or mid-term survival.