Over two-thirds of Americans access the Internet and therefore, the Internet may be an important channel for reaching the large population of sedentary individuals. The purpose of this paper is to describe the methods for a randomized controlled trial examining the efficacy of an Internet-based physical activity intervention relative to a print intervention that has been shown to be effective in previous trials. Specifically, 249 sedentary participants were randomized to receive one of three interventions: 1) Internet-based motivationally-tailored individualized feedback (Tailored Internet); 2) print-based motivationally-tailored individualized feedback (Tailored Print); or 3) physical activity websites currently available to the public (Standard Internet). Participants completed the 7-Day Physical Activity Recall interview, wore an objective physical activity monitor (i.e., ActiGraph), and participated in a treadmill fitness test at baseline, 6, and 12 months. The sample consisted of mostly women (84.2%) and Caucasian individuals (76.4%) who reported exercising an average of 21 min per week at baseline. This is the first study that we are aware of, that has examined the efficacy of a tailored Internet-based physical activity intervention. This study will have implications for the dissemination of Internet-based physical activity interventions.