A group of 9 extremely assaultive and 21 moderately assaultive male juveniles detained in a California juvenile hall were compared with control groups of 26 nonviolent delinquents detained for property offenses and 20 unmanageable 'incorrigibles.' Data came from interviews, histories, behavior observations, and completion of a variety of psychological assessment instruments. The highly aggressive acts of overcontrolled persons resulted from successive frustrations over time. However, the prediction of aggressive behavior is difficult. The usefulness of psychological tests varies with the setting in which they are used. Typical correctional institutions are not likely to correct the problems of overcontrolled offenders, who must learn to cope with and express aggressive feelings in milder ways. Extensive tabular data, survey instruments, and a 67-item bibliography are provided.