Forty-two patients developed signs of acute arterial insufficiency following percutaneous femoral angiography. Three responsible mechanisms were recognized: 1. Occlusion of the femoral artery due to stripping off of thrombus formed on the intra-arterial catheter (22 cases). 2. Distal embolization of thrombus formed at the puncture site in the femoral artery (12 cases). 3. Subintimal dissection of an atherosclerotic plaque with secondary thrombosis (8 cases). Vasospasm was not an adequate explanation for the resulting symptoms and signs of ischemia. Such a diagnosis caused delay in proper surgical therapy. Early heparinization and thrombectomy were necessary. It was successful in all but one of 35 cases. Of seven delayed cases there were complications in three.