Followup data indicate that a high percentage of the juvenile offenders engaged in serious criminal activity as adults. Most were arrested for one or more violent offenses, and over 80 percent were arrested for at least one felony offense. Delinquents whose criminal activity persisted differed from nonchronics on a wide variety of characteristics. The chronic offenders more often came from families of lower socioeconomic status, were black, had more siblings, were more retarded in school, were younger at first police contact, had longer prior records, expressed more antisocial attitudes, and were more hostile and less conforming. They also tended to be less socially mature, less intelligent, and reported greater involvement in antisocial activities. The presence of brain abnormalities should not be dismissed as a possible cause of criminality. Bizarre or aggressive fantasy content, however, did not appear to correlate with adult offenses or aggressive behavior. Chronicity can be predicted with a high degree of accuracy, but the amount of variance explained within the populations of serious offenders was small. Predictions of future violent behavior can also be made with a sufficient degree of accuracy. Implications of these and other findings and directions for further research are discussed. Tables and six references are included.