Background: The Affordable Care Act (ACA) changed the landscape of insurance coverage, allowing young adults to remain on their parents' insurance until age 26 (Dependent Coverage Provision [DCP]) and states to optionally expand Medicaid up to 133% of the federal poverty level. Although both improved insurance coverage, little is known about the ACA's impact on observed receipt of timely access to acute care. The objective of this study was to compare changes in insurance coverage and perforation rates among hospitalized adults with acute appendicitis “after vs before” Medicaid expansion and the DCP using an Agency for Healthcare Research and Quality (AHRQ)-certified metric designed to measure pre-hospital access to care. Study Design: We performed a quasi-experimental, difference-in-difference (DID) analysis of 2008-2015 state-level inpatient claims. Results: Adults, aged 19 to 64, in expansion states experienced an absolute 7.7 percentage point decline in uninsured (95% CI 7.5 to 7.9) after Medicaid expansion compared with nonexpansion states. This coincided with a 5.4 percentage point drop in admissions for perforated appendicitis (95% CI 5.0 to 5.8) that was most pronounced among young adults, aged 26 to 34, just age-ineligible for the DCP (DID: 11.5 percentage points). Medicaid expansion insurance changes were 4.1 times larger than those encountered under the DCP (DID: 1.9). They affected all population subgroups and significantly reduced access-related disparities in race/ethnicity and lower-income communities. Although both Medicaid expansion and the DCP were associated with significant insurance gains, those attributable to the DCP were more concentrated among more privileged patients. Despite this trend, both policies resulted in larger reductions in perforation rates for historically uninsured and underserved groups. Conclusions: Reductions in uninsured after Medicaid expansion and the DCP were associated with significant reductions in perforated appendix admission rates. Improvements in access to acute surgical care suggest that maintained/continued insurance expansion could lead to fewer delays, better patient outcomes, and reductions in disparities among the most at-risk populations.