BACKGROUND:While illicit drug use is prevalent among gay and bisexual men (GBM) in Australia, little is known about the factors associated with injecting drug use among GBM. METHODS:The Following Lives Undergoing Change (FLUX) study is a national, online prospective observational cohort investigating drug use among Australian GBM. Eligible participants were men living in Australia who were aged 16.5 years or older, identified as gay or bisexual or had sex with at least one man in the last year. We examined baseline data for associations between socio-demographic and behavioural characteristics and recent (last six months) injecting using log-binomial regression. RESULTS:Of 1995 eligible respondents, 206 (10.3%) reported ever injecting drugs and 93 (4.7%) had injected recently, most commonly crystal (91.4%) and speed (9.7%). Among recent injectors, only 16 (17.2%) reported injecting at least weekly; eight (8.6%) reported recent receptive syringe sharing. Self-reported HIV and HCV prevalence was higher among recent injectors than among other participants (HIV: 46.2% vs 5.0%, p < .001; HCV: 16.1% vs. 1.2%, p < .001). Recent injecting was associated with lifetime use of more drug classes (adjusted prevalence ratio (APR) = 1.31, 95% Confidence Interval (95%CI) 1.21-1.41), longer time since initiating party drug use (APR = 1.02, 95%CI 1.01-1.04), greater numbers of sex partners (2-10 sex partners: APR = 3.44, 95%CI 1.45-8.20; >10 sex partners: APR = 3.21, 95%CI 1.30-7.92), group sex (APR = 1.42, 95%CI 1.05-1.91) and condomless anal intercourse with casual partners (APR = 1.81, 95%CI 1.34-2.43) in the last six months. CONCLUSIONS:Observed associations between injecting and sexual risk reflect a strong relationship between these practices among GBM. The intersectionality between injecting drug use and sex partying indicates a need to integrate harm reduction interventions for GBM who inject drugs into sexual health services and targeted sexual health interventions into Needle and Syringe Programs.