Data indicate that the peak ages of criminality fall between the 16th and 20th birthdays. Young men under 21 account for half of all felony arrests. However, these arrest figures tend to overestimate the seriousness of the problem, as the offenses of this population tend to be less serious and occur in groups. There is a strong direct connection between juvenile criminal activity and adult criminal careers. Predictors of chronic juvenile offending include predelinquent deviant or troublesome behavior, physiological deficits associated with abnormal brain development, poor parenting, and evidence of criminal conduct or mental disorder among parents or siblings. In recent years, juvenile and criminal courts have been criticized for failing to deal severely enough with young chronic offenders. The common belief was that juvenile courts were too lenient in all types of cases because of their concern for the welfare of the minor, while criminal courts were too lenient because they did not have access to juvenile records. Analysis of case disposition patterns in Los Angeles, Las Vegas, and Seattle suggests that chronic juvenile and young adult offenders are sentenced to incarceration or State custody at least as frequently as in any other age group, at least for some offense categories, and that the seriousness of the prior juvenile record affects the severity of sentences. 54 references. (Author abstract modified).