Background: The appearance of unhealed cesarean section scar defect (CSD) has brought extensive attention in the last two decades. This study aimed to assess the relation between chronic endometritis and CSD. Methods: This study was performed on a total of sixty women who have a CSD diagnosed either by transvaginal ultrasound (TVUS) or accidentally during hysteroscopy. minute biopsies were taken from the site of the cesarean section (CS) niche and other uterine walls if it was possible. Further, histopathological examination was done, and the diagnosis of chronic endometritis was confirmed when at least one plasma cell was detected in the endometrial biopsy. Results: fifteen percent of the patients showed chronic endometritis by histopathology, while (85%) of the patients had normal histopathology. There was a statistically significant difference between histopathological findings and symptoms of CSD among studied patients, as (66.7%) of the patients who had chronic endometritis on histopathology had infertility compared to (23.5%) of patients with normal histopathology. As regards pelvic inflammatory disease, (66.7%) of the patients who had chronic endometritis had Pelvic inflammatory disease (PID) compared to (33.3%) of patients with normal histopathology. Conclusion: cesarean section scar defect may be associated with the development of chronic endometritis and may be the cause of CSDs such as infertility and PID