6020 Background: Clinical Practice Guidelines (CPGs) play an essential role in cancer care today, but there are significant concerns regarding their content and reliability. In 2011, the Institute of Medicine (IOM) report “Clinical Practice Guidelines We Can Trust” created standards for developing trustworthy CPGs. Using these standards as a benchmark, we sought to evaluate recent oncology guidelines. Methods: CPGs and consensus statements addressing the screening, evaluation or management of the four leading causes of cancer-related mortality in the US (non-small cell lung, breast, prostate and colorectal cancers) published between January 2005 and December 2010 were identified using MEDLINE. A standardized scoring system based on the eight standards set forth by the IOM was devised, and the methodology, content and disclosure policies of CPGs were critically evaluated by four independent reviewers. All CPGs were given two scores; points were awarded out of a possible 8 major criteria and 20 sub-criteria. Results: We identified 168 CPGs for inclusion in the study; 45% were from US groups. None of the CPGs fully met all the IOM standards. On average, CPGs only met 2.8 of 8 standards set forth by the IOM (mean 2.8 points out of 8, SD 1.7; 8.3 out of 20, SD 4.3). Less than half of CPGs were based on a systematic review. Only half of CPG panels addressed conflicts of interest. Overall, the CPGs were most consistent with IOM standards for transparency regarding the development process, articulation of recommendations, and use of external review. Most did not comply with standards for inclusion of patient and public involvement in the development or review process, nor did they specify their process for updating. CPGs from the US had higher overall scores than CPGs from international groups. CPGs addressing non-small cell lung cancer had higher overall scores (mean 3.9) than those for other cancers. Conclusions: The vast majority of oncology CPGs fails to meet the IOM standards for trustworthy guidelines. Notably, most CPGs are not based on systematic reviews, lack full disclosure, and do not include all relevant stakeholders in the guideline process. This highlights the need for improved CPG development processes.