Caput succedaneum is relatively common at birth but infrequently diagnosed in utero. We report the first case of a prenatal incarcerated caput succedaneum after cervical cerclage in a patient with premature rupture of the membranes(PPROM). A 41-year-old woman was referred and admitted to our hospital due to PPROM at 19 wk of gestation. Aggressive therapy, including amnioinfusion, cervical cerclage, and administration of antibiotics and tocolysis, was initiated. At 24 wk of gestation, a thumb tip-sized and polyp-like mass, which was irreducible, was delineated with a vaginal examination, vaginal speculum, and transvaginal ultrasonography, leading to the diagnosis of incarcerated caput succedaneum. Under general anesthesia, the incarcerated caput succedaneum was repositioned with fingers after cutting the string to avoid necrosis, and then, placement of a Mc Donald cervical cerclage was undertaken again. At 26 wk of gestation, she delivered a 678 g girl through an emergency cesarean section performed due to profuse bleeding and prolonged decelerations. A slight bulge with hair was observed on the head by palpation at birth. Cephalic ultrasonography, X-ray, magnetic resonance imaging and electroencephalogram confirmed no abnormality. Although the baby needed oxygen(0.2 L/min) at the time of hospital discharge, she has grown favorably at three years of corrected age. We report the first case of a prenatal incarcerated caput succedaneum after cervical cerclage in a patient with premature rupture of the membranes (PPROM). A 41-year-old woman was referred and admitted to our hospital due to PPROM at 19 wk of gestation. Aggressive therapy, including amnioinfusion, cervical cerclage, and administration of antibiotics and tocolysis, was initiated. At 24 wk of gestation, a thumb tip-sized and polyp-like mass, which was irreducible, was delineated with a vaginal examination, vaginal speculum, and transvaginal ultrasonography, leading to the diagnosis of incarcerated caput succedaneum. Under general anesthesia, the incarcerated caput succedaneum was repositioned with fingers after cutting the string to avoid necrosis, and, placement of a Mc Donald cervical cerclage was carried again. At 26 wk of gestation, she delivered a 678 g girl through an emergency cesarean sect A dumb bulge with hair was observed on the head by palpation at birth. Cephalic ultrasonography, X-ray, magnetic resonance imaging and electroencephalogram confirmed no abnormality. Although the baby needed oxygen (0.2 L / min) at the time of hospital discharge, she has grown favorably at three years of corrected age.