Background: The Affordable Care Act sought to improve access to health care for low-income individuals. This study aimed to assess whether expansion of Medicaid coverage increased rates of post-mastectomy reconstruction (PMR) for patients who had Medicaid or no insurance. Methods: A retrospective analysis performed through the National Cancer Database examined women who underwent PMR and were uninsured or had Medicaid, private insurance, or Medicare, and whose race/ethnicity, age, and state expansion status were known. Trends in the use of PMR after passage of Medicaid expansion in 2014 were evaluated. Results: In all states and at all time periods, patients with private insurance were about twice as likely to undergo PMR as patients who had Medicaid or no insurance. In 2016, only 28.7 % of patients with Medicaid or no insurance in nonexpansion states underwent PMR (p < 0.001) compared with 38.5 % of patients in expansion states (p < 0.001). Patients in expansion states also have higher levels of education, higher income, and greater likelihood of living in metropolitan areas. Additionally, patients in all states saw an increase in early-stage disease, with a concomitant reduction in late disease, but this change was greater in expansion states than in non-expansion states. Conclusions: Expansion states have larger proportions of patients undergoing PMR than non-expansion states. This difference stems from significant differences in income, education, comorbidities, race, and location. Large metropolitan areas have the largest number of patients undergoing PMR, whereas rural areas have the least.