This study evaluated the influence of tobacco possession–use–purchase (PUP) law enforcement and illicit drug use and offers. Twenty-four towns were randomly assigned into two conditions. Both conditions focused on reducing minors' access to commercial sources of tobacco. The communities assigned to the experimental condition also increased their PUP law enforcement, whereas among communities in the control condition, PUP law enforcement remained at low levels. A hierarchical linear modeling analytical approach was selected due to the multilevel data and nested design. The likelihood of a child currently using drugs, ever having used drugs, or illicit drug offers was lower in the experimental versus control conditions. These outcomes suggest that police efforts to reduce specific substance use behaviors (i.e., underage tobacco use) may have a positive spillover effect and help reduce teen drug use and illicit drug offers. © 2009 Wiley Periodicals, Inc.