Objective: To evaluate the effect of parietal peritoneal closure at cesarean delivery on adhesion formation. Methods: A prospective cohort study of women undergoing first repeat cesarean delivery was designed. All surgeons were asked immediately after surgery to score the severity and location of adhesions. Patient records were then abstracted to assess prior surgical technique, including parietal peritoneal closure, other attributes of first surgery, and patient characteristics. Exclusion criteria included adhesions, other surgery, or use of permanent suture at the first cesarean, unavailable first postoperative note and course, wound infection or breakdown following first surgery, intervening pelvic surgery, insulin-dependent diabetes mellitus, and steroid-dependent disease. The χ 2 test and multivariable logistic regression were used for statistical comparison and analysis. A total of 128 patients was required to have 80% power to detect a 50% reduction in adhesions when the parietal peritoneum was left open. Results: One hundred seventy-three patients were enrolled. Prior parietal peritoneal closure was associated with significantly fewer dense and filmy adhesions (52% versus 73% , P =.006) and significantly fewer dense adhesions (30% versus 45% , P = .043). When controlling for potential confounding variables, including prior infection, visceral peritoneal closure, rectus muscle closure, payor status, ethnicity, maternal age, gestational diabetes, and labor, parietal peritoneal closure at primary cesarean delivery was 5-fold protective against all adhesions (odds ratio 0.20, 95% confidence interval 0.08-0.49), and 3-fold protective against dense adhesions (odds ratio 0.32, 95% confidence interval 0.13-0.79). Omental-fascial adhesions were decreased most consistently. Conclusion: Parietal peritoneal closure at primary cesarean delivery was associated with significantly fewer dense and filmy adhesions. The practice of nonclosure of the parietal peritoneum at cesarean delivery should be questioned. Objective: To evaluate the effect of parietal peritoneal closure at cesarean delivery on adhesion formation. Methods: A prospective cohort study of women undergoing first repeat cesarean delivery was designed. All surgeons were asked immediately after surgery to score the severity and location of adhesions. Patient records were then abstracted to assess prior surgical technique, including parietal peritoneal closure, other attributes of first surgery, and patient characteristics. Exclusion criteria included adhesions, other surgery, or use of permanent suture at the first cesarean, unavailable first postoperative note and course, wound infection or stress following first surgery, intervening pelvic surgery, insulin-dependent diabetes mellitus, and steroid-dependent disease. The χ 2 test and multivariable logistic regression were used for statistical comparison and analysis. A total of 128 patients was required to have 80 % power to detect a 50% reduction in adhesions when the pariet Prior peritoneal closure was associated with significantly fewer dense and filmy adhesions (52% versus 73%, P = .006) and significantly fewer dense adhesions (30% versus 45%, P = .043). When controlling for potential confounding variables, including prior infection, visceral peritoneal closure, rectus muscle closure, payor status, ethnicity, maternal age, gestational diabetes, and labor, parietal peritoneal closure at primary cesarean delivery (odds ratio 0.20, 95% confidence interval 0.08-0.49), and 3-fold protective against dense adhesions (odds ratio 0.32, 95% confidence interval 0.13-0.79). Omental-fascial adhesions were decreased most consistently. Conclusion: The practice of nonclosure of the parietal peritoneum at ces arean delivery should be questioned.