The aim of this exploratory cross-sectional study was to investigate the experiences of relatives of individuals with severe mental illness with and without participation in patient-appointed Resource Group Assertive Community Treatment (RACT). A total of 139 relatives (79 with and 60 without RACT) completed the Family Involvement and Alienation Questionnaire, the Burden Inventory for Relatives of Persons with Psychotic Disturbances, and the family version of the Inventory of Stigmatizing Experiences. We found that relatives participating in RACT experienced a more positive approach from the healthcare professionals, as well as a lower degree of alienation from the provision of care. Relatives who did not participate in RACT were more afraid that their ill next of kin would hurt someone. No other differences in family burden were found. Experiences of family stigmatization were similar in both groups. In conclusion, participating in patient-appointed RACT may contribute to a higher level of satisfaction for relatives in their encounter with healthcare professionals and a more positive alliance. Implementation of RACT in new settings would require adaptation to local conditions to facilitate cooperation between healthcare staff and other relevant services. Staff training focuses on the case manager function and needs assessment, as well as how to create an alliance with the patient and his/her relatives.