At 28 weeks of amenorrhea, 1 fetus of a monoamniotic twin pregnancy died. Ultrasound and Doppler investigations of the surviving twin were normal. Three weeks later, endovaginal ultrasound and magnetic resonance imaging revealed massive bilateral cerebral ischemic necrosis in the surviving twin. In utero fetal blood sampling carried out before the termination did not reveal either anemia or thrombopenia. Current data suggest that cerebral or renal ischemic complications could set in immediately after the death of the first twin as a result of a period of acute hypotension. At least 2 weeks are necessary for them to be identifiable by ultrasound. It seems that they cannot be prevented by prompt delivery of the second twin.