Spontaneous antepartum rupture of the dividing membrane in monochorionic diamniotic twins with discordancy is extremely rare. The rupture is difficult to diagnose prenatally and has a poor outcome. The authors report a case of cord entanglement after spontaneous rupture of the dividing membrane within discordant monochorionic diamniotic twins. The subject was a 30-year-old woman pregnant with discordant monochorionic diamniotic twin at 27+4 gestational weeks. The relatively thin dividing membrane was sound until it passed parallel to the two umbilical cords where it then became ill-defined. The patient was managed cautiously due to the possibility of spontaneous rupture of the dividing membrane and potential cord entanglement. Upon delivery at 29+3 weeks due to fetal compromise, the patient presented with a monochorionic diamniotic placenta, a remnant of the disrupted dividing membrane, and entangled umbilical cords. The authors report this subject with literature review.