Accelerated longitudinal analyses revealed both similarities and differences between the developmental trajectories of empirically based aggressive versus delinquent syndromes in childhood and adolescence. Syndromes were scored from standardized ratings obtained from parents five times at 2-year intervals for seven birth cohorts of Dutch children initially assessed at ages 4 to 10 years. Scores for both the aggressive and delinquent syndromes declined from ages 4 to 10. After about age 10 years, scores for the aggressive syndrome continued to decline, but scores for the delinquent syndrome increased until about age 17. The aggressive syndrome was significantly more stable than the delinquent syndrome. Long-term predictive correlations between matched subjects from different cohorts were as high as predictive correlations between scores obtained by the same subjects, thus supporting the validity of accelerated longitudinal analyses. The results highlight important developmental distinctions between aggressive versus delinquent conduct problems. Failure to distinguish between aggressive and delinquent conduct problems could generate misleading conclusions about their respective developmental courses and limit the generalizability of results.