A research report detailing outcomes of the independent medical review process used to resolve medical disputes in the California workers’ compensation system. Results show changes in the volume of IMR determination letters for 2014 through June 2018, changes in the IMR response time by quarter, the number of decisions per letter, the IMR uphold and overturn rates since 2015, the distribution and uphold rates by medical service category, the distribution and outcomes of prescription drug IMR since 2015 with results broken out separately for dermatological and opioid IMR decisions, the distribution of 2018 IMR decisions and uphold rates, and information on the concentration of IMR determinations among high-volume providers.