Velamentous cord insertion and vasa previa occur more frequently in monochorionic twin pregnancies than in singleton pregnancies. Both have been linked with poor perinatal outcome due to the increased risk of rupture of the velamentous vessels. We present a case of acute fetal distress in 2 fetuses in a monochorionic twin pregnancy caused by ruptured vasa previa that was not detected antenatally. Both infants were severely anemic at birth. Acute blood loss in twin 1 through the ruptured vessels, led to an acute feto-fetal transfusion from the co-twin through the placental vascular anastomoses. In monochorionic twins, ruptured vasa previa and acute hemorrhage in one fetus can lead to acute feto-fetal transfusion and result in severe hypovolemic shock and acute anemia in both fetuses. Increased awareness for vasa previa and the characteristic placental angioarchitecture in monochorionic twinning is of paramount importance.