OBJECTIVE:To determine whether involvement in sporting activity in mid-adolescence would deter delinquent behaviour in late adolescence. METHODS:Members of a longitudinal cohort study were interviewed at ages 15 and 18 years and, among other topics, were asked questions relating to involvement in physical activity and delinquent behaviour. Logistic regression models were used to examine the relation between sports involvement and delinquency at age 15 years and delinquency at age 18. RESULTS:After controlling for delinquent behaviour and psychosocial factors at age 15, females with moderate or high levels of sporting activity, and males with high levels of sporting activity, were significantly more likely to be delinquent at age 18 years than those with low levels of sporting activity. No significant association was found between sporting activity and aggressive behaviour, team sport participation and delinquency, and team sport participation and aggressive behaviour. CONCLUSIONS:This study did not support the deterrence hypothesis and showed that high involvement in sporting activity, but not team sport, was associated with a subsequent increase in delinquent behaviour.