Community health centers (CHCs) are expected to play a major role in expanding primary care access under the Affordable Care Act (ACA). Although benefits of such health centers among Medicaid populations have been documented, little is known about their impact on the uninsured. Additionally, the effect of health center density on preventable hospitalizations is unknown. This study calculated health center density within five miles of California hospitals using geocoding and Haversine distance formula. Using the 2010 California inpatient dataset, rates of preventable hospitalizations were classified by Prevention Quality Indicators (PQIs). After adjusting for patient and community covariates, we found that as health center density increased, the odds ratio of preventable hospitalizations decreased in both Medicaid and uninsured patients. (OR 0.79 and 0.86 for Medicaid and uninsured respectively p<.001,.044) These findings suggest health centers are contributing to lowering preventable hospitalizations and supports plans to expand such health centers.