A 26-year-old woman at 40 weeks of gestation attended our emergency department due to sudden onset of chest and back pain, although she had experienced no previous abnormalities. The patient was very tall, had spider fingers and scoliosis, all of which indicated Marfan's syndrome. Enhanced computed tomography and cardiac ultrasonography revealed acute aortic dissection and annulo-aortic ectasia with aortic regurgitation. Thereafter, a baby weighing 3,070g was delivered by emergency Caesarean section and then a Bentall-type operation was performed consecutively. An intraoperative injection of heparin resulted in minimal uterine bleeding. Surgery at the 40th week of gestation was successful for both the mother and the neonate.