Background: To facilitate moving from evidence to recommendations, evidence grading systems (EGSs) have been developed to assess the strength of a body of evidence. This study was undertaken to systematically review existing EGSs. Objectives: To conduct a systematic review of EGSs and identify the most appropriate one for grading levels of evidence. Methods: The Evidence Report Number 47 from the Agency for Healthcare Research and Quality (AHRQ) evaluated the EGSs developed between 1979 and 2001. This comprehensive review was used as the starting point for this study. A multi-prong strategy was used to identify EGSs reported since the AHRQ search date (mid-2000), including a comprehensive search for new review articles on EGSs and individual EGSs developed from 2000 to September 2007, as well as consultation with nine experts in the area. EGSs recommended in review articles and unique EGSs from the reviews without recommendations were identified and evaluated using the AHRQ criteria for quality, quantity and consistency. A list of the highest scoring EGSs was sent to experts for consultation, and the preferred ESGs were identified based on experts’ feedback. Results: Four reviews (including AHRQ report) of EGSs were identified from 3006 citations and, after eliminating duplicates, 51 existing EGSs were identified from these reviews. Fourteen of 51 EGSs, plus nine additional EGSs identified by experts, and one identified from the 1120 citations from the search for individual EGSs, were evaluated. Six EGSs obtained highest scores and were sent to the experts for ranking by preference. Four experts ranked GRADE (2004) as the preferred ESG while another four experts ranked SIGN50 (2004) as the preferred ESG; one expert did not respond to the survey. After considering the rigorous development process, user friendliness and option of incorporating systematic reviews or metaanalyses as a level of evidence, there was consensus of the authors that the GRADE and SIGN50 systems be recommended as the preferred ESGs. Conclusions: Based on this work, the authors conclude that the GRADE and SIGN50 systems are the most appropriate EGSs for use in grading evidence for the purpose of recommendations.