Aim: TO determine the reliability of trans-abdominal and color Doppler ultrasound as diagnostic modalities in diagnosing placental invasion in patients with placenta previa with prior uterine surgery compared to those with no uterine surgery and correlation with intra operative finding. Methods: 150 pregnant women more than 28 weeks' gestation with placenta previa (75 patients with scarred uterus versus 75 patients with non-scarred uterus) were included. Routine ultrasound scan was done for evaluation of placental invasion including loss of retroplacental clear zone, abnormal placental lacunae, bladder wall interruption, myometrial thinning, placental bulge, focal exophytic mass followed by color Doppler scan to assess Doppler markers of placental invasion including uterovesical hypervascularity, subplacental hypervascularity, bridging vessels and placental lacunae feeder vessels. The results of different ultrasound and color Doppler criteria were correlated with the clinical confirmed placenta accreta or non-accreta in both groups (scarred versus non-scarred uteri). Results: There was a significant significant higher incidence of placenta accreta in scarred uterus as compared to very low incidence in non-scarred uterus. The highest sensitivities, NPVs of ultrasound markers were abnormal placenta lacunae and loss of retroplacental clear zone while the highest specificities and PPVs were myometrial thinning and bladder wall interruption as predictor of placental invasion. Bridging vessels had the highest sensitivity, specificity, PPV, NPVs and accuracy of color Doppler markers in predicting placental invasion. There was statistically significant higher incidence of ultrasound and color Doppler markers suggestive of placental invasion in scarred uterus group as compared to non-scarred group (P < 0.001) Conclusion: It could be concluded that gray scale and color Doppler ultrasound have good performance in the diagnosis of AIP and that prenatal diagnosis improves maternal outcome.