AHCPR has identified research on low back pain as a major priority. It will identify the characteristics and natural history of patients presenting to primary care physicians in the United States and the United Kingdom with acute LBP including: demographic, occupational, compensation, and clinical characteristics; patterns of diagnostic evaluation and therapies received from all sources and their perceived effectiveness; patient utilization of health care resources for back problems within 2 months of initial presentation, and outcomes at 2 months. These data will be analyzed to identify relationships between exposures, including factors present at initial presentation, therapies and utilization patterns, with outcomes including persistent pain and disability. The conduct of the study within two national primary care research networks will allow development of methods to identify cultural or country factors, particularly in the national systems of rehabilitation and disability compensation, which influence development of chronic disability. The proposed binational prospective clinical cohort study will address the need for descriptive information, create a data set for secondary analyses, and serve as a pilot for a larger international study to be conducted in the International Primary Care Network.