Online social networking is ubiquitous, but research regarding its relationship to wellbeing has yielded contradictory results. This study examined the relationship between Facebook use and wellbeing among community mental health service clients. Twenty-six clients from a community mental health service provided access to their Facebook page. Seven aspects of 3674 Facebook posts were coded, and cross-lagged multilevel models were estimated over three periods to establish the relationship between Facebook use and wellbeing over time. Some aspects of Facebook use were related to wellbeing within the same period, although this pattern of relationships did not emerge longitudinally. Although Facebook has the potential to forge social connections for those who are socially isolated, Facebook use was neither helpful nor harmful over time among people with mental health problems. Given the prevalence of social networking, a clearer understanding of its impact on wellbeing is critical for mental health providers.