BACKGROUND.: Musculoskeletal pain is a common condition, raising the concern these patients may transition to chronic opioid use. However, the incidence of and risk factors for chronic opioid use among patients with new musculoskeletal pain are not fully understood. OBJECTIVE.: To characterize the incidence and risk factors of chronic opioid use among opioid-naive patients with newly diagnosed musculoskeletal pain in the knee, neck, low back, and/or shoulder. METHODS AND FINDINGS.: The IBM® Marketscan® database provide health care utilization data for patients receiving private insurance through a participating employer or government organization. Compared to the general United States (US) population, the Marketscan® population is slightly more female and from the southern US, and less likely to come from the western US.(1) Using this data, we identified 518,195 privately insured, cancer-free, and opioid-naïve (no filled opioid prescriptions in the year prior to diagnosis) adults ages 18–64 diagnosed with non-trauma related musculoskeletal pain between January 1, 2008 and December 31, 2014 and who remained continuously enrolled for the year before and after the initial diagnosis. Since musculoskeletal pain can have varying levels of severity, we restricted our analysis to patients with pain severe enough to result in a second outpatient visit or emergency room visit for musculoskeletal pain within 30 days of the initial diagnosis date.(2) We excluded 6,036 patients with missing opioid data and 100,138 patients with conditions that could be confused for musculoskeletal low back pain (nepholithiasis, urinary tract infection, osteomyelitis, cholecystitis, osteoporosis, cauda equina syndrome, and osseous defect), resulting in a final sample of 412,021 patients.