We report a case of twin gestation (monochorionic-diamniotic) in which one of the twins was acardiac and acephalic. His co-twin suffered infectious, hematological and neurological complications. This condition belongs to the broad spectrum of twin-to-twin transfusion syndrome (TTTS) and is observed in monozygous pregnancies in which the vascular systems of the fetuses are connected. The severity of this syndrome depends on the type of anastomoses and the timing of their establishment. Circulation is accomplished by the heart of the more perfect twin ("pump twin") who is at risk for heart failure. The recipient twin may display severe and sometimes lethal anomalies, such as acardia or acephalus. In some cases a prior situation such as a single umbilical artery or chromosomal anomaly in the acardiac twin may be found. Early diagnosis is essential to formulate a plan of management focused on the normal twin.