Surrogate endpoints are commonly used outcome measuresOutcome measures used in clinical researchResearch that serve as a substitute for a more direct outcome of interest. The use of surrogate outcomesSurrogate outcomes has several advantages: they are easier and cheaper to measure, can be measured more objectively, present earlier, and require smaller sample sizesSample size than true outcomes. They also have some drawbacks, however, misleading conclusions, misrepresentation of the effect size of an interventionIntervention, and challenges in evaluating the safety of an intervention. For a surrogate endpoint to be valid, it has to meet two important criteria: there must be strong evidenceEvidence that connects the surrogate outcome to the true outcome and there must be strong clinical data available to correlate changes in the surrogate outcome with changes in the true outcome. When considering surrogate endpoints, it is important to consider potential confounders, which are third variables that independently affect two unrelated variables, causing them to be correlated despite a lack of a causal relationship. Finally, it is important to consider whether the results of a given study are valid and applicable to the specific patient in question. In this chapter, the use of surrogate endpoints in surgerySurgery is explored through a clinical example.