Family structure is one factor that can help explain drug use among adolescents. In 2005 a study was conducted with 255 ninth-grade students from an urban, predominantly Latino Los Angeles area high school. Students were 83% Latino, 58% female, and from mostly low SES households. Half of all students reported having ever used alcohol, 30% had ever smoked a cigarette, and 18% had ever used marijuana. Family structure was measured using a single open-ended question and logistic regression was employed to determine the effects of various family structures on the use of alcohol, cigarettes, and marijuana. The presence of older siblings in the home was associated with alcohol and marijuana use, and living with a cousin was associated with marijuana use. Results suggest that influential others, including siblings and cousins, should be included in measures of family structure. Study limitations are noted.