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.