Sonographically guided percutaneous thrombin injection is a minimally invasive and highly successful treatment of arterial pseudoaneurysms. Despite a very low complication rate, several severe arterial thrombotic events have been reported following thrombin injection of pseudoaneurysms. Native arterial thrombosis, though recognized as a severe complication of thrombin injection, has not been well described in the literature. Wereport a case of successful surgical management of arterial thrombosis after percutaneous thrombin injection of a femoral artery pseudoaneurysm in a 69-year-old woman. The pathophysiology, risk factors, diagnosis, and treatment options for this complication are discussed. VVC 2006 Wiley Periodicals, Inc. J Clin Ultrasound 35:88–93, 2007; Published online in Wiley InterScience (www.interscience.wiley.com).