Objective: This study intends to assess the role of placenta accreta index (PAI) score as a prenatal diagnostic tool for abnormally invasive placenta in cases of placenta previa with a history of prior cesarean. Study design: This is a prospective, noninvasive, and observational study. Setting: This study was conducted in a hospital based in Department of Obstetrics and Gynaecology, SMS Medical College, Jaipur, Rajasthan (India). Sample size and population: Eighty pregnant females presenting at or above 28 weeks of gestation with placenta previa and a history of one or more prior cesarean. Materials and methods: Cases underwent ultrasonography to find out PAI score (published in American Journal of Obstetrics and Gynecology 2014), and findings were analyzed statistically to find out appropriate cutoff value of PAI score. They were correlated with magnetic resonance imaging (MRI) and operative finding, while confirming the diagnosis histopathologically. Main outcome measures: Primary outcome was the cutoff value and diagnostic efficacy of PAI score. Secondary outcomes were fetomaternal outcomes in cases. Results: Severity of placenta accreta increased with increasing value of PAI score. On plotting receiver operating characteristic (ROC) curve, the area under curve (AUC) was found to be 0.958 with a cutoff value of >2. The sensitivity, specificity, positive predictive value, and negative predictive value of PAI score were found to be 92.86, 94.74, 95.10, and 92.30%, respectively. Conclusion: Placenta accreta index score can be a useful tool to anticipate individual patient risk, and a higher PAI score is a strong indicator of placenta accreta. Tweetable abstract: Placenta accreta index score can be used as an ultrasonographic prenatal diagnostic tool for placenta accreta.