Reducing the prevalence of adolescent cigarette smoking and alcohol drinking are public health goals of the United States. Although families have strong influence on their children, few randomized studies have examined whether family-directed programs influence those behaviors in general universal populations. This paper reports findings from an evaluation of a family program that features the mailing of four booklets to adult family members with follow-up telephone calls by health educators. A national sample of adolescent-parent pairs and a randomized experimental design were used to evaluate the program. Baseline users and nonusers of those substances were considered simultaneously in analyses so that program influences on smoking and drinking prevalence could be examined. The findings suggest that the program significantly reduced the prevalence of smoking cigarettes and drinking alcohol among adolescents. These findings are discussed in the context of earlier reports of research on the family program and implications for public health.