The relative effectiveness of continued, lapsed, and delayed smoking prevention intervention was tested with senior high school students. The original intervention was conducted during Grades 7 through 9, with significantly fewer intervention students reporting smoking than control students. The intervention was reintroduced in the 11th grade to one-half of intervention students (continued intervention), was withdrawn from the other half (lapsed intervention), and was initiated with one-half control students (delayed intervention). The 11th-grade smoking rates of these groups were compared to those of a fourth group, a continued control group. Results showed that continued control students reported significantly less smoking than continued control students and lapsed intervention students. Additionally, the delayed intervention group exhibited smoking rates lower than the lapsed intervention and continued control groups. This finding underscores the importance of continuing smoking prevention activities, as well as initiating these activities, in senior high school years.