Changes in AERP measures from childhood to adolescence were studied in 2 subgroups of hyperactive children (25 non-delinquent and 9 delinquent) and 1 group of 34 non-delinquent normal children. The 3 groups were selected on the basis of official deliquency measures obtained 8 years after their initial evaluations. All subjects were studied using the same AERP paradigm at both points in time. The major finding was that the non-delinquent hyperactive subjects were found to have abnormal maturational changes as reflected by AERP measures while the delinquent hyperactive subjects were found to have normal maturational changes in these same measures. This suggests that these 2 hyperactive groups are on a different developmental course and that they may represent different clinical entities. Results of the comparison of cross-sectional data in childhood and again in adolescence were consistent with the concept of 2 distinct subgroups.