OBJECTIVE: To better understand the mixed findings regarding the efficacy of Internet-based physical activity interventions, we examined the use and usefulness of particular website components that may lead to improvements in intervention efficacy. METHOD: Participants were sedentary individuals from a 12-month randomized controlled physical activity trial conducted in Providence, Rhode Island and Pittsburgh, Pennsylvania from 2003-2006. The present study included participants from the Tailored Internet arm (n=81; instantaneous web-based tailored feedback to participants) or the Standard Internet arm (n=82; websites currently available to the public). We obtained objective data via the intervention websites and subjective usefulness data via questionnaires. RESULTS: The Tailored Internet arm logged onto their website significantly more times than the Standard Internet arm (median 50 vs. 38; p<.05). Among participants in the Tailored Internet arm, the self-monitoring feature (i.e., logging) followed by goal setting were rated as the most useful website components. CONCLUSION: Logins in the current study were substantially higher compared to previous studies. Participants endorsed goal setting and self-monitoring as being most useful, which are critical components for health behavior change. Future studies should continue to examine these features and improve the perceived usefulness of other theory-based strategies.