OBJECTIVES: This study analyzes how frequently surrogate outcomes are used in HTAs and if the validity of these outcomes are discussed and reported within the HTAs. A surrogate outcome is defined by the National Institutes of Health as a biomarker intended to substitute for a clinical endpoint. A surrogate outcome is used when a clinical endpoint of interest is not ideal or does not occur often enough to perform meaningful statistical analysis. It is appropriate to use a surrogate outcome only when there is a strong correlation with the clinical endpoint. Before using surrogate outcomes researchers should confirm that the surrogate outcome is biologically plausible, has a magnitude of association with the clinical endpoint, and reflects changes in the relevant clinical endpoint.  METHODS: Context Matters (CM) analyzed 1,056 HTAs spanning 38 disease conditions. Each HTA had a primary outcome that could be classified as either a surrogate outcome or a clinical endpoint.  Data was analyzed for eight HTA agencies: AHRQ, DERP, SMC, HAS, PBAC, NICE, CADTH, and HIS Scotland.  For those HTAs using a surrogate outcome as the primary outcome, CM then determined if the HTA agency reported the use of the surrogate and/or discussed the surrogate outcome’s validity. RESULTS: Ninety-one percent of HTAs used a surrogate outcome (966 HTAs), but only 11% (109 HTAs) identified it as a surrogate outcome and/or discussed its validity. The agencies that discussed the use of the surrogate outcome most often were AHRQ, DERP, and HIS Scotland at 48.1%, 28.6%, and 29.0% of the time, respectively.  CONCLUSIONS: Surrogate endpoints are prevalent in HTAs, but the agencies rarely discuss the validity of these endpoints.  All agencies failed to discuss the use of the surrogate endpoint in over 50% of their reviews.  HTA agencies are not following best practice use of surrogate outcomes.