This study examined whether the risk for substance use among newly homeless young adults was associated with a history of foster care, controlling for demographics and other risk factors. Multiple logistic regression analyses, adjusted for controls, among consecutive admissions of 424 newly homeless young adults (18-21 years), determined the association between foster care and substance use. A history of foster care was reported by 35% of the sample. The most frequently used substances were alcohol, marijuana, and cigarettes. After adjusting for demographics, childhood emotional, physical, and sexual abuse, prior arrest, unemployment, lack of high school diploma, and family drug use, homeless young adults with histories of foster care were: three times as likely to smoke cigarettes (AOR=3.09); more than three times as likely to use marijuana (AOR=3.30); and almost nine times as likely to have been in drug treatment (AOR=8.81) than those without such histories. Young adults who exit foster care should be screened for substance use, particularly cigarettes and marijuana. Risk reduction interventions should be targeted and tailored to their substance prevention needs.