An hydropic fetus seen at 28-weeks gestation had a saccular aortic aneurysm in the descending thoracic aorta. Histology disclosed marked fibrointimal hyperplasia, thrombus, and attenuation of the tunica media. The remainder of the descending thoracic aorta showed fibrointimal hyperplasia. We speculate that the narrowed lumen and rigid aortic wall resulting from this vasculopathy provided an increased afterload leading to cardiac failure.