BACKGROUND: Concerns have been raised about bias in commercially supported continuing medical education (CME) activities, although the data are sparse about whether such bias exists, or if so, its extent. METHODS: Postactivity CME evaluation surveys were analyzed to quantitate reporting rates of bias, overall and by funding source. RESULTS: 5Of 1,621,647 physicians who participated in online CME activities, 1,064,642 (65.7%) completed the evaluation surveys and 5.9% reported no opinion. The affirmative rates of physician perception of bias were 0.63% overall, a weighted average of 0.84% for activities developed with and 0.48% for those developed without commercial support, a difference of 0.36% (P <.001, 95% confidence interval, 0.33-0.39). Among the subgroup who strongly disagreed that there is no bias, the difference between commercial (0.17%) and noncommercial (0.11%) funding was 0.06% (P <.001, 95% confidence interval, 0.05-0.08, P <.05), smaller than the overall difference. CONCLUSIONS: These data demonstrate that about 93% of physician participants affirmatively claim to perceive no commercial bias following online CME activities, over 99% if no opinion is included, overall and regardless of funding source.