Background Health risk behaviours are prominent in late adolescence and young adulthood, yet UK population-level research examining the relationship between drug or alcohol use and sexual health and behaviour among young people is scarce, despite public health calls for an integrated approach to health improvement. Our objective was to further our understanding of the scale of and nature of any such relationship, using contemporary data from Britain's third National Survey of Sexual Attitudes and Lifestyles (Natsal-3). Methods Analyses of data from Natsal-3, a stratified probability survey of 15162 men and women (3869 aged 16-24years), undertaken in 2010-2012, using computer-assisted personal interviewing, were carried out. Logistic regression was used to explore associations between reporting (1) frequent binge drinking (weekly), (2) recent drug use (within past 4weeks) or (3) multiple (both types of) substance use, and key sexual risk behaviours and adverse sexual health outcomes. We then examined the sociodemographic profile, health behaviours and attitudes reported by risky' young people, defined as those reporting 1 type of substance use plus non-condom use at first sex with 1 new partner(s), last year. Results Men and women reporting frequent binge drinking or recent drug use were more likely to report: unprotected first sex with 1 new partner(s), last year; first sex with their last partner after only recently meeting; emergency contraception use (last year) and sexually transmitted infection diagnosis/es (past 5years). Associations with sexual risk were frequently stronger for those reporting multiple substance use, particularly among men. The profile of risky' young people differed from that of other 16-24years old. Conclusions In this nationally representative study, substance use was strongly associated with sexual risk and adverse sexual health outcomes among young people. Qualitative or event-level research is needed to examine the context and motivations behind these associations to inform joined-up interventions to address these inter-related behaviours.