Importance: Current measures of access to care have intrinsic limitations and may not accurately reflect the capacity of the primary care system to absorb new patients. Objective: To assess primary care appointment availability by state and insurance status. Design, Setting, and Particpants: We conducted a simulated patient study. Trained field staff, randomly assigned to private insurance, Medicaid, or uninsured, called primary care offices requesting the first available appointment for either routine care or an urgent health concern. The study included a stratified random sample of primary care practices treating nonelderly adults within each of 10 states (Arkansas, Georgia, Illinois, Iowa, Massachusetts, Montana, New Jersey, Oregon, Pennsylvania, and Texas), selected for diversity along numerous dimensions. Collectively, these states comprise almost one-third of the US nonelderly, Medicaid, and currently uninsured populations. Sampling was based on enrollment by insurance type by county. Analyses were weighted to obtain population-based estimates for each state. Main Outcomes and Measures: The ability to schedule an appointment and number of days to the appointment. We also examined cost and payment required at the visit for the uninsured. Results: Between November 13, 2012, and April 4, 2013, we made 12,907 calls to 7788 primary care practices requesting new patient appointments. Across the 10 states, 84.7% (95% CI, 82.6%-86.8%) of privately insured and 57.9% (95% CI, 54.8%-61.0%) of Medicaid callers received an appointment. Appointment rates were 78.8% (95% CI, 75.6%-82.0%) for uninsured patients with full cash payment but only 15.4% (95% CI, 13.2%-17.6%) if payment required at the time of the visit was restricted to $75 or less. Conditional on getting an appointment, median wait times were typically less than 1 week (2 weeks in Massachusetts), with no differences by insurance status or urgency of health concern. Conclusions and Relevance: Although most primary care physicians are accepting new patients, access varies widely across states and insurance status. Navigator programs are needed, not only to help patients enroll but also to identify practices accepting new patients within each plan's network. Tracking new patient appointment availability over time can inform policies designed to strengthen primary care capacity and enhance the effectiveness of the coverage expansions with the Patient Protection and Affordable Care Act.