Background: Rates of PA are low among adolescents living in rural areas. Purpose: The purpose of this study is to measure 1 week of "free-living" PA via accelerometer among 9th- and 10th-grade students who reside in rural Appalachia. A second purpose was to identify gender differences in Social Cognitive Theory (SCT) variables correlated with PA. Methods: A sample (n = 633) of students from 20 different high schools in rural Appalachia wore accelerometers for 7 days. They competed a set of valid and reliable instruments assessing SCT variables. Results: Rates of PA were very low. Accelerometer assessed levels of PA were consistent with self-reported estimates published previously, but lower than estimates reported in government surveys. Several SCT variables were correlated with female PA. Only two SCT variables were not correlated with male PA. Discussion: SCT determinants of PA are different for adolescent girls and boys. The magnitude of these SCT correlates are lower than previously published studies based on self-reported PA. Translation to Health Education Practice: There is an acute need for effective instruction to promote PA among rural adolescents residing in Appalachia. A AJHE Self-Study quiz is online for this article via the SHAPE America Online Institute (SAOI) http://portal.shapeamerica.org/trn-Webinars