Background: Spaced education (SE) is a novel, evidence-based form of online learning. We investigated whether an SE program following a face-to-face continuing medical education (CME) course could enhance the course's impact on providers' clinical behaviors. Methods: This randomized controlled trial was conducted from March 2009 to April 2010, immediately following the Current Clinical Issues in Primary Care (Pri-Med) CME conference in Houston, Texas. Enrolled providers were randomized to receive the SE program immediately after the live CME event or 18 weeks later (wait-list controls). The SE program consisted of 40 validated questions and explanations covering 4 clinical topics. The repetition intervals were adapted to each provider based on his or her performance (8- and 16-day intervals for incorrect and correct answers, respectively). Questions were retired when answered correctly twice in a row. At week 18, a behavior change survey instrument was administered simultaneously to providers in both cohorts. Results: Seventy-four percent of participants (181/246) completed the SE program. Of these, 97% (176/181) submitted the behavior change survey. Across all 4 clinical topics, providers who received SE reported significantly greater change in their global clinical behaviors as a result of the CME program (p-values 0.013 to less than 0.001; effect size 0.7). Ninety-seven percent (175/179) requested to participate in future SE supplements to live CME courses. Eighty-six percent (156/179) agreed or strongly agreed that the SE program enhanced the impact of the live CME conference. Discussion: Online spaced education following a live CME course can significantly increase the impact of a face-to-face course on providers' self-reported global clinical behaviors. (Contains 2 tables, 2 figures and 1 exhibit.)