Background: Sexually transmitted infections (STIs) have been increasing among Australian Indigenous young people for over two decades. Little is known about the association between alcohol and other drug use and sexual risk behaviours and diagnosis of STIs among this population. Methods: A cross-sectional, community based self-administered survey was conducted among young Aboriginal people aged 16-29 years of age. Questionnaires included socio-demographic characteristics, knowledge, sexual risk behaviours alcohol and other drug use and health service access including self-reported history of diagnosis with a STI. Logistic regression models and population attributable risks were used to assess individual and population level impacts of illicit drug use on high risk sexual behaviours and ever reported diagnosis of an STI. Results: Of the 2877 participants, 2320 (81 %) identified as sexually active and were included in this study. More than 50 % of the study population reported that they had used at least one illicit drug in past year. Cannabis, ecstasy and methamphetamines were the three most commonly used illicit drugs in the past year. The prevalence of self-reported STI diagnosis was 25 %. Compared with people who did not report using illicit drugs, risky alcohol use and sexual behaviours including inconsistent condom use, multiple sexual partners in the past year and sex with casual partners were all significantly higher among illicit drug users. In adjusted analysis, participants who reported using illicit drugs were significantly more likely to engage in sexual risk behaviours and to ever have been diagnosed with an STI. Adjusted Odds Ratios ranged from 1.86 to 3.00 (males) and from 1.43 to 2.46 (females). At the population level, more than 70 % of the STI diagnoses were attributed to illicit drug-use and sexual risk behaviours for males and females. Conclusion: Illicit drug use in this population is relatively high compared to other similar aged populations in Australia. Illicit drug use was associated with risky sexual behaviours and STI diagnoses among this study population. Developing and implementing effective STI prevention strategies should include not only safe sex messages but also include drug and alcohol harm reduction messages.