Between February 1994 and May 1999, 100 patients (49 females, 51 males; mean age at implant 73.4 ± 7.3 years (range: 31-87 years) underwent aortic valve replacement with the Mosaic prosthesis in our department. Patients were followed up prospectively at annual intervals; the mean follow up was 2.7 years (total 273.7 patient-years (pt-yr)) and was 100% complete. Total early mortality (within 30 days) was 3.0%; the late mortality rate was 4.4%/pt-yr and included a valve-related mortality rate of 0.7%/pt-yr. The freedom from event rates at five years were 97.3 ± 1.9% for permanent neurological, 99.0 ± 1.0% for transient neurological, 95.9 ± 3.2 for thrombosed prosthesis, 95.6 ± 2.2% for anti-thromboembolic-related hemorrhage, 100% for primary valvular leak, 96.9 ± 3.0% for non-structural dysfunction, 100% for endocarditis, and 92.0 ± 4.9% for explant. The mean systolic gradients were 15.2, 13.1 and 10.1 mmHg for the 21, 23 and 25 mm valve sizes, respectively. The clinical and hemodynamic performance of the Mosaic prosthesis was highly satisfactory during the first five years after clinical introduction. Further data will be necessary to confirm long-term durability.