Back pain is a common source of disability, both from work-related injuries and from injuries that occur outside the workplace. Annually in the United States, over $15 billion is spent for the treatment of low back pain and disorders, and approximately 15 percent of the costs in workers’ compensation medical care are for low back pain cases. This study focuses on care provided or directed by physicians and addresses the following questions: What are the patterns of medical care for workers with common low back conditions in the 16 states studied? How do these patterns vary across states? How do the patterns of medical practice in the study states compare with evidence-based treatment guideline recommendations? Overall, we found that workers with similar low back conditions received very different care, depending on the state. These interstate differences were most noticeable for cases with nonspecific low back pain in the areas of diagnostic services and pain management injections. For disc cases, the interstate differences were most notable in the utilization of nerve testing, pain management injections, back surgery, and physical medicine. Large interstate differences in the timing of care were also seen for both types of low back conditions.