Childhood sexual abuse and related life traumas, and other psychosocial variables were investigated as contributors to ethnic differences in sexual risk behaviors among women who differed in HIV-serostatus. A multiethnic sample of 457 HIV-positive and HIV-negative women residing in Los Angeles county was recruited and studied over 2 years as part of the UCLA-Charles R. Drew University Women and Family Project (WFP) study. Comprehensive interviews were administered to participants by ethnically- and linguistically matched interviewers. Data on demographic information, sexual trauma, substance abuse/dependence, psychiatric distress, and sexual history and risk behaviors were collected. The sample for these analyses consisted of 155 African American, 153 European American, and 149 Latina women, and nearly two-thirds of the sample was HIV-seropositive. HIV-positive women were significantly more likely to report more posttraumatic stress, chronic stress, negative health behaviors, drug use, and psychiatric history than HIV-negative women. European American and African American women were more likely to report a history of sexual trauma than Latina women. Finally, Poisson regression analyses revealed that history of trauma, ethnicity, drug and alcohol use, homelessness, and being HIV-positive were associated with greater likelihood of engaging in high-risk sexual behaviors, with history of trauma increasing the likelihood of engaging in high-risk behaviors by 5.1%. These findings highlight important differences among women as a function of ethnicity and HIV status, and underscore the need for special services for HIV-positive women that address the risk-enhancing effects of substance abuse/dependence, homelessness, and sexual trauma.