Prosthesis-patient mismatch (PPM) occurs when the effective orifice area of the prosthesis is too small in relation to the patient's body surface area. There are few data available on the frequency and prognostic impact of PPM after transcatheter aortic valve implantation (TAVI). Our aim was to determine the prevalence of PPM and to investigate its association with medium-term clinical course of patients undergoing TAVI. We included 185 patients undergoing TAVI (79 ± 5 years, 49% male, 98% CoreValve) between April-2008 and December-2014. The effective orifice area (EOA) was determined by transthoracic echocardiography prior and after the procedure. We defined PPM as indexed EOA ≤ 0.85 cm²/m² (severe PPM if ≤ 0.65 cm²/m²). All cause death, stroke and hospitalization for heart failure were considered as major clinical events. 45 patients (24%) showed PPM (severe 11 patients, 6%). PPM was associated with a higher EuroSCORE (OR 1.06, IC 95% 1.01–1.12, p = 0.03), body surface area ≥ 1.72 m² (OR 3.58, IC 95% 1.30–9.87, p = 0.01) and small aortic annulus (OR 0.73, IC 95% 0.55–0.92, p = 0.03); and severe PPM with small prostheses size (OR 17.79, IC 95% 1.87–169.78, p = 0.012). The mean event-free survival was 34 ± 26 months. Patients with severe PPM showed lower rates of event free survival than the rest of the series (52% vs. 84%, p = 0.04) at 34 months follow up. In our series, PPM was present in a quarter of the patients after TAVI. Higher EuroSCORE, smaller prosthesis size, larger body surface area and smaller aortic annulus diameter were associated with PPM. Severe PPM was an independent factor associated with major events at medium-term follow up.