During an 11-year period we encountered 16 pregnancies in which one twin died in utero and the pregnancy continued. Eight of these twin pregnancies were monochorionic. None of the women developed severe disseminated intravascular coagulation. The fetal outcome indicates that the prognosis for a surviving dichorionic twin is relatively good, with immaturity the main hazard. By contrast the surviving monochorionic twin has a poor prognosis with a high frequency of neurological damage. This damage is not related to intrapartum or neonatal problems and at present cannot be diagnosed before birth. There is no evidence that birth of the surviving twin by caesarean section will improve the prognosis. Early diagnosis of monochorionic twins and subsequent ultrasound follow up should identify fetal growth discrepancy and possible twin to twin transfusion requiring early delivery.