Women experiencing homelessness are at heightened risk for HIV, yet risk reduction interventions specifically designed for this population are lacking. This study reports on a pilot efficacy trial of a brief evidence-based intervention, Sister To Sister (STS), that we specifically adapted for homeless women in the temporary/emergency settings where they typically seek services. Seventy-nine women, recruited from three service sites in Los Angeles County, were assigned to the 40-min adapted STS intervention or an information-only control group. At 30-day follow-up, intervention participants reported significantly greater condom use, intentions to use condoms, and sexual impulse control (as well as marginally higher positive condom beliefs and condom self-efficacy) compared to control participants. Results provide preliminary evidence that HIV risk reduction can be achieved for homeless women through a brief skill-based intervention. A randomized controlled trial employing a longer follow-up period to monitor outcomes will be necessary to determine efficacy of the adapted intervention.