BACKGROUND: Illicit drug use among gay men is common and is associated with behaviours that are at high risk for HIV transmission. METHODS: We explored illicit drug use within an ongoing cohort study of gay men living with HIV in Sydney, Australia. Most (84.3%) of the 274 New South Wales participants interviewed in 2004 for the Positive Health Cohort of HIV-seropositive gay men had used illicit drugs in the 6 months before their baseline interview. RESULTS: One in six men (17.8%) used 'party drugs' at least monthly. At 12 months' follow-up, in 2005, these patterns of illicit drug use were similar. Being younger, participating in gay 'party scenes' and engaging in 'esoteric sex practices' at baseline were associated with any and more frequent use of party drugs, both in 2004 and 2005. Illicit drug use was, however, not associated with condom use at the most recent sexual encounters. DISCUSSION: Illicit drug use appears to be highly contextual among these gay men living with HIV, and the association with risk behaviour may reflect participation in sexually adventurous subcultures as much as a direct causal effect.