Introduction: There is a steady increase in the rate of cesarean delivery. In Egypt, Cesarean sections were performed in 38.84% of deliveries in 2008, 37.88% in 2009, 39.08% in 2010, 37.72% in 2011 and 41.17% in 2012, repeated cesarean sections (RCS) was the main indication. In making plans for delivery, physicians and patients should consider a woman's chance of a successful VBAC as well as the risk of complications from a trial of labor. Approximately 60-80% of appropriate candidates who attempt vaginal birth after cesarean (VBAC) will be successful. Aim of the Work: was to determine a cut-off value that can be clinically used to allow a safe vaginal delivery by using abdominal ultrasound to evaluate the thickness of the lower uterine segment in patients with history of previous cesarean section. Patients and Methods: The lower uterine segment thickness was measured by both transabdominal ultrasound in 200 cases, gravidas (37 week – 40 week),100 cases with previous CS (study group) undergoing repeated CS, and the other 100 cases without any scar in the uterus (control group), then the grade of the scar was assessed intraoperatively. Results: By TAS the best cut- off value was 2.5 mm and this yielded a sensitivity of 77.3% and a specificity of 73.5%. At this cut-off value, the positive predictive value was 85% while the negative predictive was 62.5% and the accuracy was 76%. Conclusion: Ultrasonographic evaluation permits good assessment of the risk of scar complications intra partum. The lower uterine segment thickness is related to the grade of the scar. The best timing to perform the scan is at late third trimester. A cut-off value of 2.5 mm by TAS can be safely used with high degree of sensitivity and specificity.