This study has explored how family members of care recipients define and sustain claims of mistreatment in old-age care. Twenty-one informants were recruited from an association of relatives of care recipients in Sweden. Using argumentation analysis, four warrants about mistreatment were identified from the qualitative interview data: they referred to physical harm, psychological harm, social-care deficiencies and identity subversion. The first three categories are similar to those recognised in previous research on elder mistreatment, but the fourth, which is described in detail in the article, is less familiar: elder mistreatment as the violation of an older person's identity. The family members backed their claims about staff members' violation of a care recipient's persona or identity by using arguments that drew on their unique knowledge of the care recipient's appearance, daily routines and preferred activities. They also described their attempts to protect the dignity and identity of a care recipient, their fears of abuse, and actual cases of conflict and retribution by care staff. They consistently positioned themselves as guardians of identity through their claims of mistreatment. The study provides important knowledge about family members' moral view of elder mistreatment, which may enhance the understanding of conflicts between formal care providers and family members.