A patient with Marfan's syndrome was seen at 29 weeks' gestation with acute aortic dissection. She underwent aortic root replacement under deep hypothermia and circulatory arrest. The fetal heart rate was ominous during surgery but recovered later. Serial ultrasonographic examinations showed progressive fetal brain atrophy. The patient was delivered at 38 weeks' gestation of a girl weighing 2305 g, in whom severe spastic tetraplegia, absent psychomotor development, and therapy-resistant epilepsy developed. This is the first case to document progressive fetal brain atrophy after cardiac surgery in pregnancy.