INTRODUCTION: Medicaid expansion's (ME) impact on postoperative outcomes after abdominal surgery remains poorly defined. We aimed to evaluate ME's effect on surgical morbidity, mortality, and readmissions in a state that expanded Medicaid (Virginia) compared to a state that did not (Tennessee) over the same time period. METHODS: Virginia Surgical Quality Collaborative (VSQC) American College of Surgeons National Surgical Quality Improvement Program data for Medicaid, uninsured, and private insurance patients undergoing abdominal procedures before Virginia's ME (3/22/18-12/31/18) were compared with post-ME (1/1/19-12/31/19), as were corresponding non-ME state Tennessee Surgical Quality Collaborative (TSQC) data for the same 2018 and 2019 time periods. Postexpansion odds ratios for 30-d morbidity, 30-d mortality, and 30-d unplanned readmission were estimated using propensity score-adjusted logistic regression models. RESULTS: In Virginia, 4753 abdominal procedures, 2097 pre-ME were compared to 2656 post-ME. In Tennessee, 5956 procedures, 2484 in 2018 were compared to 3472 in 2019. VSQC's proportion of Medicaid population increased following ME (8.9% versus 18.8%, P < 0.001) while uninsured patients decreased (20.4% versus 6.4%, P < 0.001). Post-ME VSQC had fewer 30-d readmissions (12.2% versus 6.0%, P = 0.013). Post-ME VSQC Medicaid patients had significantly lower probability of morbidity (-8.18, 95% confidence interval: -15.52 ∼ -0.84, P = 0.029) and readmission (-6.92, 95% confidence interval: -12.56 ∼ -1.27, P = 0.016) compared to pre-ME. There were no differences in probability of morbidity or readmission in the TSQC Medicaid population between study periods (both P > 0.05); there were no differences in mortality between study periods in VSQC and TSQC patient populations (both P > 0.05). CONCLUSIONS: ME was associated with decreased 30-d morbidity and unplanned readmissions in the VSQC. Data-driven policies accounting for ME benefits should be considered.