Study Objective: To examine the correlation between the occurrence of adenomyosis and the outcome of vaginal repair of cesarean scar defects (CSD). Design: A retrospective observational cohort study. Setting: University hospital. Patients: A total of 278 women with CSD were enrolled at the Shanghai First Maternity & Infant Hospital between January 2013 and August 2017. Interventions: Vaginal excision and suture of CSD. Measures and Main Results: According to preoperative magnetic resonance imaging (MRI) findings, patients were divided into two groups, the adenomyosis group (group A) and the non-adenomyosis group (group B). For group A patients, the mean duration of menstruation at 3- and 6-months follow-up was shorter and the TRM at the median-month follow-up was significantly thinner than those in group B patients (p < 0.05). There were more patients with class-A healing in group B compared with group A (44.7% vs 30.0%; p < 0.05). Furthermore, 59.3% (32/54) of women tried to conceive after vaginal repair. The pregnancy rates of women with and without adenomyosis were 66.7% (8/12) and 61.9% (26/42), respectively. The duration of menstruation decreased significantly from 13.4 ± 3.3 days to 7.6 ± 2.3 days after vaginal repair in 25 patients (p < 0.001). The TRM increased significantly from 2.3 ± 0.8 mm to 7.6 ± 2.9 mm after vaginal repair (p < 0.001). Conclusion: Vaginal repair reduced postmenstrual spotting and improve fertility in patients with CSD. Adenomyosis might be an adverse factor in the repair of uterine incisions.