Using data from a national survey of adolescent substance use, this study examined whether adolescents with varied patterns of alcohol and cigarette use differed in their estimates of the likelihood they would use an illegal drug in the future. While nonusers of either substance were the most likely to indicate that they would never use drugs in the future, users of both substances were the most likely to indicate that they would use drugs. In addition, while users of both were most likely to indicate that they were likely to use illegal substances, only-smokers were more likely than only-drinkers to indicate that they were likely to use such substances in the future. The article discusses these findings in terms of the gateway theory of drug sequencing and cognitive precursors of experimentation with illegal substances. Because the original questionnaire did not ask about the use of illicit substances, adolescents who had already experimented with such substances could not be eliminated from analysis of study results. Future researchers exploring intention-to-use differences in adolescents should include questions regarding use of both licit and illicit substances. Tables, references