Until the recent introduction of therapeutic amniocentesis, pregnancies complicated by the stuck twin phenomenon usually suffered poor outcomes. We report the first case in which a single amniocentesis of the cotwin was followed by equalization of amniotic fluid volume in both sacs, resolution of nonimmune hydrops in the cotwin, and delivery of 2 healthy infants. The cause of the phenomenon in this was most likely severe twin-twin transfusion, based on a negative hematologic and serologic immune and nonimmune hydrops evaluation, and placental histology revealing a superficial large-caliber arteriovenous anastomosis joining the twins’ circulations without an intervening capillary bed. The mechanism proposed for the physiologic response in this case to therapeutic amniocentesis is based on the correction of abnormal amniotic fluid volumes and pressures. This contention is supported by histologic evaluation of the placenta and the intrapartum fetal heart rate tracin