This study aimed to develop reliable scales of HIV vaccine attitudes. Gay men were recruited at the 2001 Sydney Gay and Lesbian Mardi Gras Fair Day, a large gay community gathering of thousands of people. A total of 776 participants completed a questionnaire containing 38 items about HIV vaccines. Factor analysis of the responses of 585 HIV-negative/untested men revealed four distinct factors (accounting cumulatively for 24.5% of the variance): I, Comfort with Participation in HIV Vaccine Trials, Cronbach alpha = 0.81; II, Confidence in HIV Vaccines/Vaccine Trials, Cronbach alpha = 0.71; III, Sexual Freedom, Cronbach alpha = 0.64; IV, Willingness to Participate in HIV Vaccine Trials, Cronbach alpha = 0.59. Of the HIV-negative/untested men, 162 (27.7%) were likely/very likely to volunteer for HIV vaccine trials, and 422 (72.3%) were unlikely/very unlikely to do so. As preliminary evidence of construct validity, the 162 men had a higher mean score on scale I (2.79), indicating greater comfort with trial participation than their 422 counterparts (2.47, p < 0.001). As preliminary evidence of concurrent validity, the 162 men had a higher mean score on scale IV (2.79), indicating greater willingness to participate than the rest (2.22, p < 0.001). Alongside HIV vaccine trials, these scales may be a useful adjunct to social research in gay communities; to monitor and be responsive to community concerns about HIV vaccine trials as well as their potential to undermine safe sex practices.