Diagnosing placenta percreta can be difficult. We describe a 41-year-old woman presenting at 21 weeks' gestation with intraabdominal bleeding and no signs of placental abnormality on ultrasound. The disagreement between results of the ultrasound and magnetic resonance imaging made definitive diagnosis difficult. The bleeding resolved spontaneously after a blood transfusion, and the patient was hospitalized for the remainder of the pregnancy. Delivery was by scheduled repeat cesarean at 34 weeks' gestation. Spontaneous rupture of the entire fundus occurred at the time of delivery. Placenta percreta was confirmed by histologic examination of the operatively excised uterus.