BackgroundMultiple risk behaviours (MRBs), typically beginning in adolescence, are associated with increased risk of adverse health and social outcomes. The association between autism and MRBs is little understood.MethodsData were from the Avon Longitudinal Study of Parents and Children, an UK-based longitudinal, birth cohort study. Exposures were diagnosed autism and four autistic traits: social communication difficulties, pragmatic language, repetitive behaviours and reduced sociability. Outcomes were participation in up to 14 risk behaviours, including alcohol consumption, smoking, risky sexual behaviours and physical inactivity. Outcome data were collected at ages approximately 12, 14, 16 and 18.ResultsUp to 4300 participants were included in latent basis growth curve analyses with adjustment for confounders. Social communication difficulties were associated with an above average level of MRBs engagement at ~12 years (mean differenceβ0.26; 95% CI 0.13–0.40), and above average rate of engagement from ages ~12–18 (β0.08; 95% CI 0.02–0.13). Repetitive behaviours were associated with above average levels of engagement in MRBs at ~12 years (β0.24; 95% CI 0.09–0.38). Contrastingly, reduced sociability was associated with a reduced rate of engagement in MRBs from ages ~12–18 (β−0.06; 95% CI −0.11 to −0.02). In sex-specific analyses, persisting differences in MRB engagement patterns from ages ~12–18 were observed in males with social communication difficulties and females with reduced sociability temperament.ConclusionsHaving elevated levels of some autistic traits appear to have differentiated effects on MRB engagement patterns. These findings could reflect difficulties fitting in and/or coping mechanisms relating to difficulties with fitting in.