Background Amniotic band syndrome is a rare phenomenon, but it can result in serious complications. We report herein our experience of amniotic band syndrome in a monochorionic diamniotic twin pregnancy where rupture of the dividing membrane occurred early in the second trimester. Case Presentation A 29-year-old nulliparous woman was referred to us for management of her monochorionic diamniotic twin pregnancy at 10 weeks of gestation. When we were unable to identify a dividing membrane at 15 weeks of gestation using two-dimensional ultrasonography, we used three-dimensional ultrasonography to confirm its absence. Both modalities showed that the left arm of baby B was swollen and attached to a membranous structure originating from the placenta at 18 weeks of gestation. Tangled umbilical cords were noted on magnetic resonance imaging at 18 weeks of gestation. Emergency cesarean delivery was performed at 30 weeks of gestation because of the nonreassuring fetal status of baby A. The left arm of baby B had a constrictive ring with a skin defect. Both neonates had an uncomplicated postnatal course and were discharged around 2 months after delivery. Conclusions Attention should be paid to the potential for amniotic band syndrome if rupture of the dividing membrane between twins is noted during early gestation.