Childhood electrophysiological and clinical measures were obtained in 110 hyperactive (HA) and 76 normal children, who were later followed up as adolescents. Official arrest data were obtained on all subjects and used to measure outcome. The usual interpretation, that the presence of a brain function abnormality suggests a poor prognosis, does not apply to the clinical EEG, EEG spectral and ERP measures obtained on these HA boys. In fact, the converse was found to be true, that is EEG and ERP measures abnormalities were associated with a good outcome, while normal values of these measures were associated with a poor outcome. Data were presented that suggest that there may be two distinct subgroups of HA boys. The first group was characterized by abnormalities in childhood brain function, abnormal changes in brain function with age, less antisocial and hyperactive behavior in childhood, and absence of delinquency in adolescence. The second group was characterized by normal childhood brian function, normal changes in brain function with age, more antisocial and hyperactive behavior in childhood, and teenage delinquency. Childhood EEG and ERP measures were found to be significantly different in these delinquent and non-delinquent HA groups, while social, familial and cognitive attributes were not. The N2 amplitude of the AERP in delinquent hyperactive (DHA) boys was found to be significantly larger than in the non-delinquent hyperactive (NDHA) boys. This N2 amplitude may prove clinically useful in selecting HA boys for delinquency prevention programs.