To examine differences in the correlates, comorbidity and use of services between aggressive and delinquent children and adolescents.An Australian representative sample (n = 4083) of parents of children and adolescents were administered a psychiatric diagnostic interview, the Child Behaviour Checklist, and other instruments to measure service use. The characteristics of children with high scores (top 5%) in the aggressive and delinquent syndromes or both were then examined.The proportion of aggressive children decreased with increasing age while that of delinquents increased. The aggressive group was specifically associated with the impulsive-hyperactive subtype of attention deficit hyperactivity disorder (ADHD) (OR = 12.63; 95% CI = 5.97-26.74). Comorbidity between ADHD, aggression and delinquency was less frequent among adolescents than in children, with the exception of the inattentive subtype in which comorbidity was higher. Both aggressive and delinquent groups had a considerable overlap with conduct disorder. Aggressive and delinquent youths used services more often, but parents perceived aggressive children as more in need of help than delinquent ones. Living in a sole parent family was specifically associated with the delinquent group (OR = 3.34; 95% CI = 2.25-4.96).The results suggest that these empirically derived syndromes while sharing many features also differ in important ways, highlighting the need for further convergence between categorical and dimensional classifications. Their differential association with the subtypes of ADHD requires further examination and may help to understand the relationship between ADHD and conduct problems. The importance of aggressive behaviour in children should not be underestimated since it is associated with significant psychopathology, parental distress and use of services.