A 39-year-old woman who had undergone an uncomplicated elective cesarean section for a low-lying placenta collapsed and died the following day. At autopsy, there was dissection of an aneurysmally-dilated thoracic aorta with 400 mls of fluid and clotted blood in the pericardial sac. There were no features of Marfan syndrome or other connective tissue disorders. Histology revealed thinning of the aortic wall with fragmentation of elastic fibers and no inflammation. Vessels elsewhere were normal. This case demonstrates a rare complication of pregnancy that may not present until after delivery with unexpected collapse and sudden death. Predisposing factors include an increased cardiac output, reduction in systemic vascular resistance, an increase in left ventricular muscle mass, and alterations in serum progesterone and estrogen levels which may cause structural changes to the aortic wall. The possibility of syndromic and familial connective tissue disorders should also be considered.