Participants were homeless youths in the greater Seattle metropolitan area. Adolescents ages 13 to 21 who were not in the custody of the State and whose residence was unstable were eligible for participation. A total of 374 (54 percent male and 46 percent female) eligible youths agreed to be interviewed. Participants were asked about physical and sexual victimization, and they also responded to questions on PTSD that corresponded with the DSM-IV PTSD symptoms. Within the full sample, most homeless youths were exposed to at least one form of physical or sexual victimization since leaving home (82.7 percent). Many were physically but not sexually victimized (44.2 percent); some were both physically and sexually victimized (31 percent); and a few were sexually but not physically victimized (6.4 percent). Among victimized youths (n=301), 17.7 percent had symptoms consistent with a diagnosis of PTSD. A total of 21.4 percent of the females and 14.7 percent of males manifested PTSD symptoms. Results from a confirmatory factor analysis suggest that disaggregating symptoms of avoidance from symptoms of emotional numbing provides a better fit of the data than the current DSM-IV model of PTSD, in which these symptoms are combined in one factor. Medical care, safe places to stay, legal support, and counseling and therapy may be helpful for physically victimized youths. Immediate services, such as referrals to sexual assault clinics or testing and treatment for sexually transmitted diseases, may be necessary for those who are raped. Sexually exploited youths may need material support to decrease dependence on their perpetrators for food or places to stay. They may also need legal support to prosecute perpetrators, as well as long-term emotional support to cope with their trauma experience. Appropriate PTSD interventions that are relatively brief or that are likely to promote stability in a highly transient population may be beneficial. Study limitations and future directions are discussed. 3 tables and 40 references