Objective <p>To estimate the risk of cesarean scar diverticulum associated with the timing of cesarean section.</p> Patients and Methods <p>This was a retrospective cohort study involving three Chinese hospitals. A total of 11,132 women were included in this study. They were divided into three groups according to the timing of cesarean section: before labor (group A), the first stage of labor (group B), and the second stage of labor (group C). Data of interest were extracted from the medical records and compared among groups. The logistic regression was conducted to estimate the odds ratio and to adjust for confounders.</p> Results <p>For the entire study cohort, a total of 1134 (10.2%) women had a cesarean scar diverticulum after cesarean section. The number of cesarean scar diverticulum for Groups A, B, and C was 397 (7.8%), 313 (8.7%), and 424 (17.4%), respectively. The differences among groups were statistically significant (<i>P</i> &lt; 0.001). After adjusting for the influence of potential confounding factors, the multivariate analysis shows that compared with the cesarean section before labor, the cesarean section after full dilation of the cervix significantly increases the risk of cesarean scar diverticulum (aOR: 2.67, 95% CI: 1.31–4.99, <i>P</i> = 0.015) and symptomatic cesarean scar diverticulum (aOR: 2.45, 95% CI: 1.21–4.67, <i>P</i> = 0.012).</p> Conclusion <p>Cesarean section during the second stage of labor significantly increases the risk of cesarean scar diverticulum.</p>