A 25-year-old male with Marfan Syndrome and previous aortic root surgery presented with severe chest and upper back pain. Initial CT angiogram showed mild aortic dilatation but no acute dissection. Anti-impulse therapy was initiated. Five days after presentation, follow-up CT angiography revealed a new pseudoaneurysm of the descending thoracic aorta. The patient underwent replacement of the mid-descending thoracic aorta with a collagen-impregnated woven polyester tube graft without complication. Despite negative initial imaging and relatively small aortic size, patients with Marfan Syndrome with acute chest pain should be treated with high suspicion and may benefit from admission and serial imaging.