The presence of acute peripartum anaemia in a monochorionic twin pregnancy represents a clinical challenge requiring prompt recognition and management. Twin-to-twin transfusion syndrome (TTTS) is a major complication of these pregnancies and a medical emergency in its acute form. Acute intrapartum fetoplacental transfusion (AIFT) has been reported infrequently. The authors present a case of a probable acute TTTS in an uneventful monochorionic monoamnionic twin pregnancy, where typical ultrasound criteria for long-standing TTTS were absent. The first twin was born pale, hypotonic and developed hypovolemic shock due to acute anaemia. Soon after birth, she presented with seizures and a cerebral ultrasound detected a large parieto-occipital infarction. The second twin, although plethoric, was clinically well. The risk of acute TTTS and AIFT, although infrequent and unpredictable, should be kept in mind when planning delivery of monochorionic twins, because the consequences for one or both twins can be disastrous.