BACKGROUND: Social networking sites such as Facebook afford new opportunities for behavior-change interventions. Although often used as a recruitment tool, few studies have reported the use of Facebook as an intervention component to facilitate communication between researchers and participants. The aim of this study was to examine facilitator and participant use of a Facebook component of a community-based intervention for parents. METHODS: First-time parent groups participating in the intervention arm of the extended Infant Feeding, Activity and Nutrition Trial (InFANT Extend) Program were invited to join their own private Facebook group. Facilitators mediated the Facebook groups, using them to share resources with parents, arrange group sessions, and respond to parent queries. Parents completed process evaluation questionnaires reporting on the usefulness of the Facebook groups. RESULTS: A total of 150 parents (from 27 first-time parent groups) joined their private Facebook group. There were a mean of 36.9 (standard deviation 11.1) posts/group, with the majority being facilitator posts. Facilitator administration posts (e.g., arranging upcoming group sessions) had the highest average comments (4.0), followed by participant health/behavior questions (3.5). The majority of participants reported that they enjoyed being a part of their Facebook group; however, the frequency of logging on to their groups' page declined over the 36 months of the trial, as did their perceived usefulness of the group. CONCLUSIONS: Facebook appears to be a useful administrative tool in this context. Parents enjoyed being part of their Facebook group, but their reported use of and engagement with Facebook declined over time.