The twin-twin transfusion syndrome is a rare but severe complication in monozygotic twins. A total of 172 twin pregnancies were investigated in our hospital between January 1990 and August 1993. The patients were divided into 4 groups: Group I: Normal twin pregnancy, treatment only in our hospital. Group II: Twin-twin transfusion syndrome, treatment only in our hospital. Group III: Normal twin pregnancy, delivery in another hospital. Group IV: Twin-twin transfusion syndrome, after treatment and therapy delivery in another hospital. These cases were analysed concerning prenatal management and perinatal outcome. The perinatal mortality rate in group I-IV was 17%, 58%, 18% and 60%, respectively. A benefit of aggressive amniocentesis in case of polyhydramnios, administration of digoxin and timing of labour could be demonstrated.