Objective: This research examines how access to information on peer health behaviors affects one’s own health behavior. Methods: We report the results of a randomized field experiment in a large corporation in which we introduced walkstations (treadmills attached to desks that enable employees to walk while working), provided employees with feedback on their own and their coworkers’ usage, and assessed usage over 6 months. We report how we determined our sample size, and all data exclusions, manipulations, and measures in the study. Results: Walkstation usage declined most when participants were given information on coworkers’ usage levels, due to a tendency to converge to the lowest common denominator—their least-active coworkers. Conclusion: This research demonstrates the impact of the lowest common denominator in physical activity: people’s activity levels tend to converge to the lowest-performing members of their groups. This research adds to our understanding of the factors that determine when the behavior of others impacts our own behavior for the better—and the worse.