In recent years, the California workers' compensation system has been encumbered by rising costs and high utilization of medical care. To address these concerns, the California legislature passed a series of initiatives that call for the use of evidence-based medical-treatment guidelines concerning, at a minimum, the frequency, duration, intensity, and appropriateness of all treatment procedures and modalities commonly performed in workers' compensation cases. The American College of Occupational and Environmental Medicine (ACOEM) guidelines were adopted as presumptively correct until alternative plans could be evaluated and a decision made about which guidelines to adopt for the long term. This report presents an evaluation of the medical guidelines that might be used to determine the appropriateness of care provided California's injured workers. The study identified 72 guidelines for work-related injuries, which were then screened using multiple criteria. Five comprehensive guideline sets were found to satisfy the requirements of the legislation and the preferences of the state. A comparative evaluation was made of both the technical quality and clinical content of the selected guidelines. Based on the results of the evaluation, recommendations are presented for actions the state might take in the short term, the intermediate term, and the longer term.