The aim of the study was to explore how family members of care recipients define mistreatment in old age care. Twenty one interviewees where recruited from a Swedish association for relatives of care recipients. Using argumentation analysis, four warrants about mistreatment were identified—warrants about physical harm; warrants about psychological harm; warrants about social deficiencies; and warrants about identity subversion. Particular interest was devoted to the way family members backed claims about the violation of a care recipients’ person or identity by using arguments about a unique knowledge of appearance, daily routines and preferred activities. Family members also related incidents from attempts to guard the dignity and identity of a care recipient to fear of and actual cases of conflict and retribution from members of the caring staff. The study provides important knowledge about the phenomenon of mistreatment and may enhance the understanding of conflicts between formal care providers and family members.