Social identity theory proposes that a threatened social identity can impact on self-concept and well-being. As a low-status minority group, mental health service users face the possibility of a threatened social identity compounding existing mental health problems. This may be further complicated by an inpatient admission where the context in which social identity is maintained has changed from a community setting. We use a qualitative approach to explore the salient social identity of mental health inpatient service users using semi-structured interviews. Analysis showed that the salient in-groups and out-groups mainly centred around the inpatient context but were somewhat influenced by non-mental health service group membership. Participants also talked of their unique characteristics as group members. How these findings relate to social identity theory and, particularly how they relate to mental health service users within changing contexts is explored.