OBJECTIVES: The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) working group defines patient values and preferences as the relative importance patients place on the main health outcomes. We provide GRADE guidance for assessing the risk of bias and indirectness domains for certainty of evidence about the relative importance of outcomes. STUDY DESIGN AND SETTING: We applied the GRADE domains to rate the certainty of evidence in the importance of outcomes to several systematic reviews, iteratively reviewed draft guidance and consulted GRADE members and other stakeholders for feedback. RESULTS: This is the first of two articles. A body of evidence addressing the importance of outcomes starts at "high certainty"; concerns with risk of bias, indirectness, inconsistency, imprecision, and publication bias lead to downgrading to moderate, low, or very low certainty. We propose subdomains of risk of bias as selection of the study population, missing data, the type of measurement instrument, and confounding; we have developed items for each subdomain. The population, intervention, comparison, and outcome elements associated with the evidence determine the degree of indirectness. CONCLUSION: This article provides guidance and examples for rating the risk of bias and indirectness for a body of evidence summarizing the importance of outcomes.