Acute severe twin-twin transfusion syndrome occurs in about 1% of monochorionic twin gestations. In the most severe form, acute hydramnios develops in the recipient twin's sac and fetal hydrops may be present. The donor twin is anemic and oligohydramnios is present, so that the donor appears "stuck" in a cocoon made by its adherent amnion. In this report, aggressive therapeutic amniocentesis restored amniotic fluid volume to normal in both sacs in all pregnancies. Fetal hydrops resolved in three of five (60%) of the fetuses affected. Pregnancy was extended a mean 80 +/- 33 days (+/- 2 SD) and perinatal survival was 79%. These findings contrast dramatically with the virtual 100% mortality reported in the literature with no therapy. Repeated aggressive amniocentesis effectively reversed the physiology of twin-twin transfusion syndrome and should be the treatment of choice for acute hydramnios, which previously had no recommended therapy.