INTRODUCTION: Since 2000, notifications of HIV and other sexually transmitted infections (STIs) have increased significantly in Australian gay men. We evaluated the impact of a social marketing campaign in 2008-2009 aimed to increase health-seeking behavior and STI testing and enhance HIV/STI knowledge in gay men. METHODS: A convenience sample of 295 gay men (18-66 years of age) was surveyed to evaluate the effectiveness of the campaign. Participants were asked about campaign awareness, HIV/STI knowledge, health-seeking behavior, and HIV/STI testing. We examined associations between recent STI testing and campaign awareness. Trends in HIV/STI monthly tests at 3 clinics with a high case load of gay men were also assessed. Logistic and Poisson regressions and χ tests were used. RESULTS: Both unaided (43%) and aided (86%) campaign awareness was high. In a multivariable logistic regression, awareness of the campaign (aided) was independently associated with having had any STI test within the past 6 months (prevalence ratio = 1.5; 95% confidence interval = 1.0-2.4. Compared with the 13 months before the campaign, clinic data showed significant increasing testing rates for HIV, syphilis, and chlamydia among HIV-negative gay men during the initial and continued campaign periods. CONCLUSION: These findings suggest that the campaign was successful in achieving its aims of increasing health-seeking behavior, STI testing, and HIV/STI knowledge among gay men in Victoria.