<p>Abstract</p> <p>Background</p> <p>The amount of medical education offered through the Internet continues to increase, providing unprecedented access for physicians nationwide. However, the process of evaluating these activities is ongoing. This study is a continuation of an earlier report that found online continuing medical education (CME) to be highly effective in making evidence-based decisions.</p> <p>Methods</p> <p>To determine the effectiveness of 114 Internet CME activities, case vignette-based surveys were administered to U.S.-practicing physicians immediately following participation, and to a representative control group of non-participants. Survey responses were analyzed based on evidence presented in the content of CME activities. An effect size for each activity was calculated using Cohen's <it>d </it>to determine the amount of difference between the two groups in the likelihood of making evidence-based clinical decisions.</p> <p>Results</p> <p>In a sample of 17,142 U.S. physicians, of the more than 350,000 physicians who participated in 114 activities, the average effect size was 0.82. This indicates an increased likelihood of 48% that physicians participating in online activities were making clinical choices based on evidence.</p> <p>Conclusion</p> <p>Physicians who participated in online CME activities continue to be more likely to make evidence-based clinical choices than non-participants in response to clinical case vignettes.</p>