Objectives. We examined the associations between posttraumatic stress disorder (PTSD) and HIV risk behaviors among a random sample of 241 low-income women receiving care in an urban emergency department. Methods. We recruited participants from the emergency department waiting room during randomly selected 6-hour blocks of time. Multivariate analyses and propensity score weighting were used to examine the associations between PTSD and HIV risk after adjustment for potentially confounding sociodemographic variables, substance use, childhood sexual abuse, and intimate partner violence. Results. A large majority of the sample self-identified as Latina (49%) or African American (44%). Almost one third (29%) of the participants met PTSD criteria. Women who exhibited symptoms in 1 or more PTSD symptom clusters were more likely than women who did not to report having had sex with multiple sexual partners, having had sex with a risky partner, and having experienced partner violence related to condom use in the preceding 6 months. Conclusions. The high rate of PTSD found in this sample and the significant associations between PTSD symptom clusters and partner-related risk behaviors highlight the need to take PTSD into account when designing HIV prevention interventions for low-income, urban women