BACKGROUND
Adolescents often experiment with substance use and sexual activity, which can impact upon their health and well-being, and establish harmful patterns of behavior which continue into adulthood. While substance use and participation in sexual behaviors often co-occur, few studies have examined whether these behaviors cluster in adolescence.

OBJECTIVE
To investigate clustering of sexual activity and substance use among youth in Northern Ireland.

METHOD
Data from 875 young people (aged 16) who participated in the 2008 Northern Ireland Life and Times Survey were used to investigate clustering using the Odds/Expected ratio method. Gender differences in clustering were explored.

RESULTS
Alcohol consumption was the most prevalent risk behavior (75%), followed by cigarette smoking, sexual intercourse, illicit substance use, and solvent use the least prevalent. Over 40% of young people participated in multiple risk behaviors (2 or more). Several behavior combinations were statistically clustered, for most the reported prevalence was lower than expected, however, participation in all five risk behaviors occurred at a much higher rate than expected, particularly for male youth.

CONCLUSIONS
While experimentation with risky behaviors is often considered developmentally appropriate in adolescence it is important to understand how young people experience these behaviors, and the potential for multiple risk exposures as a result of participation in substance use and sexual behaviors. These findings highlight the clustering of substance use and sexual behaviors, and indicate variations in vulnerability to participation in multiple risk behaviors by gender.