This paper reports on a social marketing campaign directed toward high-risk men who have sex with men (MSM) in Toronto and Ottawa to: encourage testing for HIV and syphilis; improve knowledge about HIV transmission, seroconversion symptoms, and the HIV window period; and heighten awareness of syphilis transmission and its relationship to facilitating HIV transmission. Evaluation data were collected from a large-scale online pre-and post-campaign survey of sexually active MSM and from laboratory testing data. Men who turned up to be tested also filled out an exit survey. The campaign websites attracted some 15,000 unique visitors, 54% of whom had an IP address in Toronto or Ottawa. Laboratory data showed a 20% increase in HIV testing in Toronto over the campaign compared to the previous year. The overall rate of HIV-positive tests remained relatively constant. Knowledge levels about seroconversion symptoms, STI and HIV transmission, and the HIV window period were significantly better among post-campaign survey respondents aware of the campaign compared to post-campaign respondents who were not aware, and compared to pre-campaign respondents
