Background: The prevention provision of Affordable Care Act (ACA) mandates private insurance to waive cost sharing for preventive services with grade A or B recommendations from the US Preventive Services Task Force. Although several professional societies have recommended augmenting screening mammography with MRI for women at high risk for breast cancer, the ACA prevention provision does not apply to screening MRI. This study examined the proportion of high-risk women having zero cost sharing associated with breast MRI for screening purposes and estimated out of pocket (OOP) costs as well as sources of variations. Methods: We identified women who underwent MRI and mammography for breast cancer screening from Marketscan database, 2009-2017. We quantified OOP costs as the sum of copayment, coinsurance, and deductible and defined zero cost sharing as having no OOP cost. We calculated the proportion of zero cost sharing for mammography and that for MRI and compared the time trend of each before and after ACA (enacted in 2010). We used multivariable logistic regression to examine factors associated with zero cost sharing for MRI use. We estimated OOP costs of MRI and examined cost variations by geographic regions or whether a woman had high deductible plans. Results: 25,232 women were included in the analysis. For screening mammography, the rate of zero cost sharing increased from 81% in 2009 to 91% in 2011 (post ACA) then 97% in 2017. For MRI, the rate was 41%, 37%, and 25%, respectively. The odds ratio (OR) of zero cost sharing for MRI screening was significantly lower for women with high deductible plans (OR = 0.65, 95% CI: 0.59-0.72) and for those resided in South (vs. Northeast) region (OR = 0.50, 95% CI: 0.46-0.53), after controlling for age, MSA, family breast cancer history, and year. OOP costs of MRI varied by region and insurance plan (Table); the mean OOP cost for women with high deductible plan were more than twice the mean cost for those in other plan types. Conclusions: With the financial protection under the ACA prevention provision applying to only screening mammography, many women at high risk for breast cancer are subject to high OOP costs for MRI screening. Those enrolled in high deductible plans and resided in the South are especially vulnerable financially.