We are reporting the case of a 63 year-old woman presenting an early thrombosis of a mechanical aortic Saint-Jude prosthesis, on the 21st post-operative day, following an insufficient anti-coagulant treatment and discovered by the presence of a well tolerated murmur of aortic insufficiency. The treatment consisted in fibrinolysis using urokinase, administered intravenously at a dose of 4,400 IU/kg/hour, for 12 hours. The clinical, ultrasound and radiocinematographic control performed on the 75th day, were normal; the patient, at that time being treated with anti-vitamin K and platelets anti-aggregates. No complication was observed. This case demonstrates the advantages of fibrinolytic treatments in early thrombosis following insertion of a valvular prosthesis.