Homeless youth experience disproportionately high rates of trauma and posttraumatic stress disorder (PTSD). This study examined correlates of trauma and PTSD among homeless youth with a focus on the impact of homeless culture, substance addiction, and mental health challenges. Homeless youth (N = 146) from Los Angeles, California, Denver, Colorado, and St. Louis, Missouri, were recruited from organizations providing services to homeless youth using comparable methods. Results indicate that 57% of respondents had experienced a traumatic event and 24% met criteria for PTSD. A multinomial logistic regression model revealed greater transience, alcohol addiction, mania, and lower self-efficacy predicted PTSD whereas trauma exposure was associated with alcohol addiction only. Findings have implications for screening and intervening with traumatized homeless youth across service settings.