Subjects were 81 male Latino gang members aged 14 to 18 incarcerated in Los Angeles Probation Camps. The following variables were used to ascertain the extent of trauma leading to the diagnosis of posttraumatic stress disorder (PTSD): social support, alienation, level of gang identification, level of exposure to violence, and alcohol and other drug use. Gang members who were exposed to a greater degree of violence showed more PTSD symptomatology and overall psychological symptomatology than did those who were not so exposed. No significant differences were found between high and low levels of social support, alienation, or alcohol and other drug abuse. Alienation, level of drug use, and number of drugs used closely approached significance. Gang members who identified with the gang more were more exposed to traumatic violence and showed more PTSD symptomatology than did those who were less exposed. The best predictor for PTSD was frequency of exposure to traumatic violence. Twelve percent of the subjects met the criteria for DSM-IIIR diagnosis of PTSD. 9 appendixes, 131 references