Consistent with the common-sense model of self-regulation, illness representations are considered the key to improving health outcomes for medically unexplained symptoms and illnesses (MUS). Which illness representations are related to outcomes and how they are related is not well understood. In response, we conducted a meta-analysis of the relationship between illness representations, self-management/coping, and health outcomes (perceived disease state, psychological distress, and quality of life) for patients with MUS. We reviewed 23 studies and found that threat-related illness representations and emotional representations were related to worse health outcomes and more negative coping (moderate to large effect). Generally, increases in negative coping mediated (with a moderate to large effect) the relationship of threat/emotional illness representations and health outcomes. Protective illness representations were related to better health outcomes, less use of negative coping and greater use of positive coping (small to moderate effect). The relationship of protective illness representations to better health outcomes was mediated by decreases in negative coping (moderate to large effect) and increases in positive coping (moderate effect). Perceiving a psychological cause to the MUS was related to more negative health outcomes (moderate to large effect) and more negative emotional coping (small effect). The relationship of perceiving a psychological cause and more negative health outcomes was mediated by increases in negative emotional coping. Improving our understanding of how illness representations impact health outcomes can inform efforts to improve treatments for MUS. Our results suggest behavioural treatments should focus on reducing threat-related illness representations and negative coping.