Accelerated longitudinal analyses revealed both similarities anddifferences between the developmental trajectories of empiricallybased aggressive versus delinquent syndromes in childhood andadolescence. Syndromes were scored from standardized ratings obtainedfrom parents five times at 2-year intervals for seven birth cohorts ofDutch children initially assessed at ages 4 to 10 years. Scores forboth the aggressive and delinquent syndromes declined from ages 4 to10. After about age 10 years, scores for the aggressive syndromecontinued to decline, but scores for the delinquent syndrome increaseduntil about age 17. The aggressive syndrome was significantly morestable than the delinquent syndrome. Long-term predictive correlationsbetween matched subjects from different cohorts were as high aspredictive correlations between scores obtained by the same subjects,thus supporting the validity of accelerated longitudinal analyses. Theresults highlight important developmental distinctions betweenaggressive versus delinquent conduct problems. Failure to distinguishbetween aggressive and delinquent conduct problems could generatemisleading conclusions about their respective developmental coursesand limit the generalizability of results.