Aortic thrombi are commonly present in atherosclerotic and aneurysmatic aortas. Thrombus formation in an aorta with or focal atherosclerosis in a patient without risk factors is rare. A 63-year-old woman with dementia and hypothyroidism presented with hypotension and respiratory distress. Work-up revealed leukocytosis, sinus tachycardia, and proximal small bowel obstruction. At emergent laparotomy, a superior mesenteric artery thomboembolus was identified with necrosis of surrounding bowel. The patient expired on hospital day five. Autopsy revealed a 1.4 cm thrombus overlying an isolated atherosclerotic plaque in the ascending aorta and infarctions of the spleen, liver, and right kidney as well as occlusive thromboembolism of the superior mesenteric artery. This case report illustrates lethal complications from an unsuspected aortic thrombus. Work-up for patients presenting with signs of peripheral embolization, or in this case, necrotic bowel, should include the aorta as a source of embolic thrombi.