Background: Maternal and fetal mortality and morbidity from placenta previa and placenta accreta present a challenge to the obstetricians and were related with high demands on health resources. With the increase incidence of caesarean sections combined with the increasie of maternal age, the cases of placenta praevia with complications, will continue to increase. Aim of the Work: This study aimed to find out diagnostic value of Placenta Accreta Index Score (PAIS) in prenatal diagnosis of morbidly adherent placenta. Patients and methods: The study was carried at ultrasound unit of obstetrics and gynecology department in Zagazig university hospitals. The study involved 92 cases of placenta previa delivered at zagazig university hospitals. Study Design is Prospective descriptive study. Results: It was found that placenta accreta significantly increased, with increase No. of previous C.S , anterior placenta previa, increase grading of placental lacunae, presence of vascularity in placenta-bladder interface and with obliteration of uteroplacental demarcation, It was found that there is a significant impact of PAIS in diagnosis of placenta accrete. Conclusion: The application of the Placenta Accreta Index may be helpful in predicting individual patient risk for morbidly adherent placenta and significantly improved the antenatal detection of morbidly adherent placenta compared to prior standard interpretation.