The youths were all referred by their parents to the head instructors of Tae Kwon Do clubs in several different States. They were identified as delinquents by their scores on the Minnesota Multiphasic Personality Inventory (MMPI). They received training under one of three different protocols for 6 months. One group received training in traditional Tae Kwon Do; one in a 'modern' version that did not emphasize the psychological and philosophical aspects of the sport; and one group, the control group, in physical activity with the instructor. The first group showed decreased aggressiveness, lowered anxiety, increased self-esteem, increased social adroitness, and an increase in value orthodoxy, as indicated by pretest and posttest scores on the Jackson Personality Inventory (JPI). They also had normal MMPI scores at the end of the study. In contrast, the second group showed an increased tendency toward delinquency on the MMPI, greatly increased aggressiveness, and opposite effects from the first group on the JPI. The control group showed no notable differences on any of the personality measures. Figure, table, and 30 references. (Author abstract modified)