Activity-based group work is widely used by occupational therapists in mental health settings (Lloyd, King, & Bassett, 2002), but the evidence to support this intervention is unclear. We therefore conducted a systematic review focused on the question, “Is activity-based group work effective in helping people with severe and enduring mental illness in community settings improve their functional ability and/or reduce their mental health symptoms?” We used a wide-ranging search strategy, including electronic searching, hand searching, citation searching, and use of gray literature, and identified 136 potentially relevant papers. After assessment of relevance and quality, only 3 articles met the minimum criteria. Heterogeneity and flaws in quality meant it was not possible to make specific inferences for practice from the studies. Large-scale rigorous research, in the form of randomized controlled trials, is urgently needed to identify whether activity-based group work is effective.