Purpose: To explore the experience of belonging to a self-advocacy group for people with intellectual disabilities, and how membership of such a group impacts on individual members. Methods: Eight people with intellectual disabilities, who belonged to a self-advocacy group for at least 6 months, were interviewed about their experiences of membership. A grounded theory approach was used to generate and analyse the interview data. Results: A model of the impact of belonging to a self-advocacy group for people with intellectual disabilities on individual members' self-concept is developed. The model proposes that participants' self-concept changes as a result of group membership and that this process of change involves six key categories: joining the group; learning about and doing self-advocacy; becoming aware of group aims and identity; experiencing a positive social environment; identifying positive change in self-concept and seeing the future of self and group as interlinked. Conclusion: Membership of a self-advocacy group for people with intellectual disabilities changes the self-concept of participants. The processes surrounding these changes have important implications for self-advocacy groups both, in recruitment and in supporting group members.