The natural history of 11 cases of twin–twin transfusion syndrome (TTTS) in monochorionic diamniotic (MCDA) twin pregnancies has been reviewed. Seven cases before 28 weeks and four pregnancies after 28 weeks had been followed up without intervention. Eight cases had premature uterine contractions. All seven pregnancies before 28 weeks aborted, leading to a 100% mortality rate. After 28 weeks all mothers delivered live births. The diagnosis of TTTS before 28 weeks, and with premature uterine contraction, seems to be a poor prognostic sign.