Background Mental health disorders (MHD) are becoming more recognized in pregnancy. Whether MHD are associated with health services utilization postpartum is incompletely understood. Objective To investigate postpartum emergency department (ED) use within 30 days of delivery among women with preexisting MHD during pregnancy. Study Design This was a retrospective cohort study evaluating ED use among postpartum women with or without MHD who delivered at an academic center between January 2014 to June 2018. Demographic and outcome data were chart abstracted and analyzed. Multivariate regression was performed to adjust for covariates. Results During the study period, 13,605 women delivered at the institution, 2,355 (17.3%) of whom had an underlying MHD. The primary diagnoses of MHD were anxiety (48.8%), depression (34.8%), substance use disorder (11.4%), bipolar disorder (3.4%), psychosis (0.7%), and other (0.8%). There were a total of 565 ED visits within thirty days of delivery. Women who presented to the ED postpartum were more likely to have public insurance, identify as Black or Asian and have an underlying MHD. Among women with MHD, 155 (6.6%) utilized the ED within 30 days of their delivery compared to 410 (3.6%) of patients without MHD (p<0.001; aOR 1.74 95%CI [1.42-2.13]). When assessing the risk of ED usage per type of MHD, anxiety (aOR 1.73 (95%CI [1.31-2.27]) and depression (aOR 2.13 (95% CI [1.59-2.86]) carried the highest risk. Compared to women without MHD, women with underlying MHD had more presentations for hypertension (15.5% vs. 11.2%) and psychiatric evaluations (4.5% vs. 0.2%, both p<0.001). Conclusion Women with mental health disorders utilize the ED during the postpartum period for psychiatric and obstetric reasons more frequently compared to women without mental health disorders. Increased surveillance, treatment, and follow-up during pregnancy and the early postpartum period may be warranted for this high-risk population.