This article presents preliminary evaluation findings from Parent Party Patrol (PPP). PPP is a two-hour single-session intervention that provides information to parents about ways to increase monitoring and improve communication and family guidelines regarding substance use, with the goal of reducing adolescent involvement in unsupervised activities and associated substance use. Seventy-three attendees from 15 PPP sessions completed baseline and three- to six-month follow-up information. At follow-up, participants showed significantly increased awareness of adolescent substance use and unchaperoned activities, improved communication and use of family guidelines regarding substance use, and increased monitoring of their children's activities. A significant reduction in adolescent attendance at unchaperoned parties was also reported. Replication of the study with a larger, more representative sample and controlled design is suggested. As adolescent substance use is a multidetermined problem, PPP may be best viewed as one part of a broader comprehensive substance abuse prevention program.