In a sample of 506 adjudicated boys, 316 (62 percent) were or had been gang members. They displayed the following psychological attributes: (1) a set of attitudes associated with inadequate or disturbed socialization; (2) attitudes and opinions of persons in lower socioeconomic classes such as the ethic of the tough and the premature adoption of adult behavior; (3) a tendency to distort reality according to their personal needs or desires; (4) distrust of and estrangement from others, especially those representing authority; (5) anger and frustration and discomfort concerning the presence and control of these emotions; (6) reluctance to acknowledge unpleasant events or conditions in everyday life; (7) psychotic behavior; (8) emotional instability; (9) unhappiness and a sense of being victimized; and (10) social adventurism, sensation seeking and impulsive behavior. The article discusses gang structure, subcultural orientation and ethnic makeup, and causal models. Notes, tables, references, appendix