About half of Americans have at least one chronic disease, and chronic diseases account for nearly 90% of healthcare expenditures in the US. Primary care can reduce potentially preventable hospitalizations and overall costs of chronic diseases. However, only about 3% of US healthcare spending is on prevention. Racial/ethnic disparities and income disparities have been well documented in the use of primary care. The ACA expanded insurance coverage for millions of Americans and included a mandate that all insurance plans must cover recommended preventive services at no cost to the patient. Literature shows the ACA resulted in an increase in access to care, but results on utilization rates of primary care post-ACA are mixed. Using nationally representative data sets from 2009-2015, I examined the utilization rates of preventive services among vulnerable populations after the full implementation of the ACA, and how Medicaid state policy and expansion under the ACA affected the utilization of preventive services among vulnerable populations. Next, using the Maryland Medical Care Database from 2012-2014, I examined how continuity of primary care affects the odds of having any hospitalization as well as potentially preventable hospitalizations. I found that the ACA was associated with an increase in preventive services recommended yearly, and the ACA was not associated with disparities in preventive service utilization among vulnerable populations. Additionally, I found that state Medicaid policies on preventive services were associated with increased utilization of flu shot, but Medicaid expansion was not associated with increased utilization of preventive services or many changes in disparities in preventive service utilization among vulnerable populations. Finally, I found that primary care, especially ongoing primary care, was strongly associated with a decrease in the odds of having any hospitalization and potentially preventable hospitalizations. Results suggest that increased access alone will not increase utilization rates and reduce health disparities, but rather, a focus on education of what coverage options are available through the ACA, the importance of ongoing primary care, and how to navigate the healthcare system once insured could increase utilization of preventive care, especially in vulnerable populations.