Context-Efforts to promote organ donation have traditionally relied on mass-mediated or interpersonal communication to promote donor registration. Despite its popularity, the use of online media has yet to be carefully evaluated as a platform to promote organ donation. Objective-To describe results of an intervention to promote donor registration that relies solely on online media to communicate to target audiences. Design-For 3 years, 6 campaigns were implemented in 3 different online media formats. Setting-Online media formats included (1) traditional online advertising, (2) student seeders' social networking sites campaigns, and (3) challenge campaigns. Participants-Online media campaigns primarily targeted college-aged individuals. Intervention-Each campaign directed individuals to the dedicated project website, where they could access educational material about donation and request a donor registration card. Main Outcome Measures-Unique website visitors, webpages viewed per site visit, time spent on site, and organ donor cards requested/received were tracked in relation to each online media format. Results-Traditional online advertising offered greater message exposure but failed to result in a higher proportion of website visitors who registered their donation intentions. Use of student seeders (ie, motivated students who promote donation by using social networking sites) and challenge campaigns resulted in greater attention to the project website, donor card requests, and subsequent returns. Additional research is recommended to reveal the effect of combining 2 or more varying online media formats within a single campaign. (Progress in Transplantation. 2012; 22:168-174) (C) 2012 NATCO, The Organization for Transplant Professionals doi: http://dx.doi.org/10.7182/pit2012931