This case report describes a cervico-isthmic pregnancy which presented at our institution at 24 weeks. The diagnosis was not recognised until delivery. Ultrasounds performed late in the second trimester, following preterm rupture of membranes, suggested placenta percreta. The patient was prepared for the likelihood of hysterectomy at the time of delivery, which was planned as caesarean section. Semi-elective surgery undertaken at 26 weeks gestation due to developing chorioamnionitis revealed the diagnosis of cervicoisthmic pregnancy. Following delivery of a live-born infant, massive haemorrhage ensued, necessitating hysterectomy and transfusion.