The long-term results (5 to 12 years) of 77 patients with Smeloff-Cutter aortic valve prostheses are reported. These patients were comparable in age, preoperative clinical condition and type of aortic valve replacement. The postoperative follow-up period of this series was however significantly longer. The 5 year survival rate was of 87%. The causes of death included thromboembolism, infectious endocarditis and cardiac failure. Mortality was higher in the first 5 postoperative years : 2,4% patient-years compared to 1,5% patient-years in the following years. Thromboembolism and neurological complications were particularly rare, representing a risk of 1,04% patient-years but these complications were lethal in half the cases in which they occurred. No haemolytic complications were observed. Infective endocarditis always occurred in patients with a history of infection, the complication usually being late (after 3 years). The life expectancy of patients seen after 5 years is at least 5 additional years in 80% of cases. The haemodynamic profile of the prosthesis did not degrade with time. After 5 years, 58,6% of patients in functional Class IV at operation were in Class I or II afterwards. 84,4% of patients operated in functional Class III were in Class I or II, and 93% operated in functional Class II were in Class I or III. A control of 3 prostheses carried out by the Cutter laboratory after 10 and 11 years' function shows practically no deterioration of the prosthesis. The low incidence of thromboembolism, the absence of haemolysis and long-term deterioration of the prosthesis are particularly valuable characteristics of this prosthesis in the aortic position.