Concern internationally that young gay men are at increased risk of HIV infection has not been reflected in earlier findings in Australia where younger men have not been found to be at increased likelihood to engage in unprotected anal intercourse with casual partners (UAIC). There has, however, been little attention paid to the issue of age in relation to HIV risk behaviour in Australia in recent years. In 2007, among men who completed Gay Community Periodic Survey questionnaires in Sydney, Melbourne and Brisbane, Australia, younger men were more likely to report being in relatively short-term monogamous relationships than were their older counterparts. They were also less likely to know their own or their partners' HIV serostatus. Men aged less than 25 years reported fewer recent partners and were less likely to report sex with casual male partners in the previous six months (p<0.001). Younger men were also less likely to engage in group sex. Approximately, one-quarter of the sample reported engaging in any UAIC in the previous six months during each year of the survey. Younger men were no less likely to report UAIC overall, but they were somewhat more likely to report taking the receptive position during UAIC. While age is a consideration in the assessment of risk of HIV transmission among gay men, this risk is dependent upon the context in which it occurs: Age mixing may be an important consideration in understanding HIV risk among young gay men.