BACKGROUND: A significant number of American youth do not participate in sufficient levels of physical activity. METHODS: This article reports the association between the availability of commercial physical activity-related facilities and self-reported physical activity behavior among United States adolescents. Geographic identifiers at the ZIP-code level were used to combine repeated cross-sections of individual-level data on 8th-, 10th-, and 12th-grade adolescents from the Monitoring the Future (MTF) Survey with external commercial physical activity-related facility outlet density measures obtained from business lists from Dun and Bradstreet for the years 1997 through 2003. The estimation samples based on questions from different survey forms included a total of 195,702 observations on which information on physical activity (sports, athletics, or exercise) was available and 58,876 observations on which information on vigorous exercise behavior was available. RESULTS: The results showed a statistically significant but very small association between local-area per capita availability of commercial physical activity-related facilities and physical activity behavior among U.S. adolescents. An additional local-area facility per 10,000 capita was associated with only a 0.22 percentage point increase in frequent vigorous exercise among the full sample of adolescents. By gender and grade level, the study found significant associations among female and older students: increasing availability from a low (1 facility) to a high (8 facilities) number of local-area facilities was associated with a 6.6% and 9.0% increase in frequent physical activity and frequent vigorous exercise among 12th-grade girls, respectively, and a 6.4% increase in frequent vigorous exercise among 12th-grade boys. CONCLUSIONS: Improving the availability of commercial physical activity-related opportunities among underserved populations may help to increase activity levels among older adolescents and girls.