We perceived a need for relatives’ evaluation of geriatric care and rehabilitation during the care period as well as the first few weeks after discharge. The aim of this study was therefore to develop and test a questionnaire for use in telephone interviews with relatives of patients discharged from geriatric wards to measure their perceptions of the quality of care. The instrument development process comprised a literature review, focus group interviews, construction of items, test of content validity, a pilot study and finally the main data collection to test the construct validity and reliability. A Likert-type questionnaire was used containing 26 items with five response alternatives; totally disagree, partly disagree, doubtful, partly agree and totally agree. The main data collection comprised 238 telephone interviews. The factor analysis revealed four factors with an eigenvalue >1.0. Cronbach’s alpha coefficient was 0.89, which indicates high reliability. The duration of the telephone interview was approximately 10–20 minutes. The relatives appreciated the opportunity to evaluate the care, and a majority stated that they preferred a telephone interview to answering in writing. The questionnaire is considered reliable, valid and useful for identifying areas in need of quality improvement interventions.