OBJECTIVE: To develop and test the reliability of a tool for rating websites that provide information on evidence-based medicine. DESIGN: For each site, 60% of the score was given for content (eight criteria) and 40% was given for organization and presentation (nine criteria). Five of 10 randomly selected sites met the inclusion criteria and were used by three observers to test the accuracy of the tool. Each site was rated twice by each observer, with a 3-week interval between ratings. SETTING: Laval University, Quebec city. PARTICIPANTS: Three observers. MAIN OUTCOME MEASURES: The intraclass correlation coefficient (ICC) was used to rate the reliability of the tool. RESULTS: Average overall scores for the five sites were 40%, 79%, 83%, 88%, and 89%. All three observers rated the same two sites in fourth and fifth place and gave the top three ratings to the other three sites. The overall rating of the five sites by the three observers yielded an ICC of 0.93 to 0.97. An ICC of 0.87 was obtained for the two overall ratings conducted 3 weeks apart. CONCLUSION: This new tool offers excellent intraobserver and interobserver measurement reliability and is an excellent means of distinguishing between medical websites of varying quality. For best results, we recommend that the tool be used simultaneously by two observers and that differences be resolved by consensus.