The increasing visibility of support groups has prompted a flurry of sociological investigation, much of which explores how groups benefit participants. What researchers have failed to consider is the group itself. Bringing social movement theory to bear on the case of eating disorder support groups, this study seeks to explore how support groups attract and sustain adequate participation. Participant observation in an eating disorder support group reveals that broad diagnostic and prognostic frames, coupled with strong motivational framing and collective identification on the basis of a shared disordered self, promote support group participation. The very processes that enable support groups' successful mobilisation, however, simultaneously construct a collective illness identity, which in turn serves as the basis for participants' individual‐level identity work. More specifically, support group mobilisation processes construct eating disorders as highly consequential, highly symptomatic, chronic, rooted in the self, and uncontrollable. Such findings suggest that support groups may have unanticipated and potentially adverse consequences for participants and thus build on previous work highlighting the unintended health consequences of framing processes. Such findings further contribute to our understanding of how macro‐social forces shape illness experience.