Study Objective Determine whether patients with endometriosis have a greater likelihood of morbidity at cesarean section. Design Retrospective cohort study Setting Academic hospital Patients or Participants Patients with a singleton pregnancy resulting in primary cesarean delivery between 01/01/2015-12/31/2018. Women with history of surgically-confirmed endometriosis were matched 1:3 to women never diagnosed with endometriosis on delivery year and whether the cesarean was indicated for myomectomy history. Endometriosis was sub-categorized into rASRM stage I/II or stage III/IV by operative findings. Composite morbidity was defined by any transfusion, hysterectomy, or organ injury at cesarean. Additional outcomes included placenta previa, accreta, total surgical time for cesarean, and time from incision to hysterotomy. Multivariable logistic regression models adjusting for age, race, gravidity, IVF conception, and operative hysteroscopy quantified odds ratios(OR) and 95% confidence intervals(CI). Interventions N/A Measurements and Main Results Study population included 384 patients (rASRM stage I/II=44, III/IV=52, no endometriosis=288). Composite morbidity was clinically and statistically significantly greater (17% versus 6%; OR=3.90,CI=1.37-11.05) for stage III/IV patients compared to women without endometriosis. The stage III/IV group also had higher odds of previa (13% versus 3%; OR=4.94,CI=1.45-16.78) and trended towards increased accreta (11% versus 1%; OR=10.18,CI=1.85-55.88) compared to women without endometriosis. Odds of composite morbidity and abnormal placentation were similar comparing stage I/II endometriosis patients to women without endometriosis. Time from skin to uterine incision did not differ between either endometriosis group and women without endometriosis, while stage III/IV patients were more likely to have a surgical time >1 hour (OR=2.49,CI=1.21-5.11). Conclusion Among patients who had a singleton pregnancy resulting in primary cesarean delivery, women with a history of stage III/IV endometriosis had greater odds of placenta previa, and surgical morbidity compared to patients without endometriosis. These findings suggest that one or more characteristics of rASRM stage III/IV may be related to abnormal placentation and morbidity at cesarean delivery, and endometriosis phenotypes should be better documented and further explored.