Common concerns about guidelines relate to the quality of the evidence base that supports them (1), a lack of clarity about the degree to which opinion rather than evidence shapes the recommendations (2), conflicts of interest among guideline developers (3–4), inadequate recognition of the heterogeneity of patient characteristics and preferences (5), and the feasibility of implementation (6). Such concerns and a charge included in the Medicare Improvements for Patients and Providers Act of 2008 prompted the Institute of Medicine (IOM) to release a set of rigorous standards for developing high-quality clinical practice guidelines (7). Table 1 highlights the characteristics that the IOM believes define trustworthy guidelines. Some of the proposed standards address issues long recognized as important: the supremacy of evidence over opinion, the importance of disclosure and management of potential conflicts of interest among guideline developers, and the requirement that guideline reports include a clear description of the development process. Other proposed standards address processes that few guideline groups have yet adopted, such as the inclusion of patient representatives in the development process, an open public comment period, and a clear plan for guideline updates. All in all, the IOM sets a high bar, and strict application of the standards would classify many, if not most, clinical guidelines as untrustworthy.