ABSTRACT: BACKGROUND AND OBJECTIVES:Before 2014, low-income individuals in the United States with non-dialysis-dependent CKD had fewer options to attain health insurance, limiting their opportunities to be preemptively wait-listed for kidney transplantation. We examined whether expanding Medicaid under the Affordable Care Act was associated with differences in the number of individuals who were pre-emptively wait-listed with Medicaid coverage. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS:Using the United Network of Organ Sharing database, we performed a retrospective observational study of adults (age≥18 years) listed for kidney transplantation before dialysis dependence between January 1, 2011-December 31, 2013 (pre-Medicaid expansion) and January 1, 2014-December 31, 2016 (post-Medicaid expansion). In multinomial logistic regression models, we compared trends in insurance types used for pre-emptive wait-listing in states that did and did not expand Medicaid with a difference-in-differences approach. RESULTS:States that fully implemented Medicaid expansion on January 1, 2014 ("expansion states," n=24 and the District of Columbia) had a 59% relative increase in Medicaid-covered pre-emptive listings from the pre-expansion to postexpansion period (from 1094 to 1737 listings), compared with an 8.8% relative increase (from 330 to 359 listings) among 19 Medicaid nonexpansion states (P<0.001). From the pre- to postexpansion period, the adjusted proportion of listings with Medicaid coverage decreased by 0.3 percentage points among nonexpansion states (from 4.0% to 3.7%, P=0.09), and increased by 3.0 percentage points among expansion states (from 7.0% to 10.0%, P<0.001). Medicaid expansion was associated with absolute increases in Medicaid coverage by 1.4 percentage points among white listings, 4.0 percentage points among black listings, 5.9 percentage points among Hispanic listings, and 5.3 percentage points among other listings (P<0.001 for all comparisons). CONCLUSIONS:Medicaid expansion was associated with an increase in the proportion of new pre-emptive listings for kidney transplantation with Medicaid coverage, with larger increases in Medicaid coverage among racial and ethnic minority listings than among white listings.