OBJECTIVES: Reducing avoidable hospitalizations is a major target of recent health care reform efforts. Increasing the supply of primary care providers has been proposed as one way to reduce hospitalizations. There is little empirical evidence, however, that has linked increased availability of primary care to reduced hospitalizations.  Further, it is unknown if primary care availability has the same effect on hospitalization rates for the uninsured as the insured. The purpose of this study is to examine the association between primary care availability, all-cause hospitalizations, and admissions for three common types among nonelderly adults (ambulatory care sensitive conditions, mental health and substance abuse, and mandatory admissions). METHODS: Using data from the 2009 Healthcare Cost and Utilization Project (HCUP) State Inpatient Databases (SID) we examined variations in inpatient hospitalizations between the insured and uninsured across Core Based Statistical Areas (CBSAs) in 44 states. We also explored the association between primary care availability and hospital use by insurance status while controlling for patient, population and market factors using a broad definition of primary care. Poisson regression models were used to estimate the relationship between primary care availability and the rate of hospitalizations by insurance status. RESULTS: Primary care supply is generally linked to lower hospitalizations across conditions. Areas with more community health centers and rural health clinics were linked to greater hospital use among the uninsured. CONCLUSIONS: The findings from our study highlight some of the complexities and nuanced relationship between the supply of primary care providers and hospitalizations by insurance status. The availability of primary care alone may not be enough to reduce the differences in hospital use. Policies that take into consideration the availability of primary care in addition to issues of accessibility, appropriateness, and effectiveness may mitigate differences in hospital utilization between populations.