BACKGROUND/OBJECTIVE: To evaluate the validity and reliability of a patient-reported measure of the "age-friendliness" of health care. DESIGN: Based on four essential domains of high-quality health care for older outpatients (Medications, Mobility, Mentation and "what Matters," i.e., the 4 M's), we drafted a five-item questionnaire for older outpatients to rate the age-friendliness of their health care. One question addressed each of the 4 M's; the fifth addressed the overall age-friendliness of their care. After feedback from healthcare professionals, quality improvement experts, and a patient-caregiver focus group, we revised the items to create the Age-Friendliness Questionnaire (AFQ). SETTING We tested the AFQ by appending it to two surveys. PARTICIPANTS: Older outpatients in Idaho during July to October 2019: Survey 1, with 23 other items, was sent to 1,257 older patients who were medically complex; Survey 2, with 35 other items, was sent to 2,873 older patients who visited outpatient primary care providers (PCPs) during the specified time period. MEASUREMENTS: Respondents rated their providers' performance using a 1 to 5 ("never" to "always") scale for each of the five items (possible AFQ scores = 5-25). RESULTS: The response rates were 41.4% and 33.3%, respectively. In Survey 1, the mean AFQ score from patients who had received care from a geriatrics consult clinic was higher than that from patients who had received their care from PCPs (19.3 vs 15.6; P < .001), and AFQ scores correlated with other quality-of-care scores. In Survey 2, AFQ scores predicted respondents' likelihood of recommending their providers to others (P < .001). The AFQ exhibited high internal reliability (interitem correlations = .49-.77; Cronbach's α = .89). CONCLUSION: The AFQ appears to be a valid and reliable measure of the age-friendliness of outpatient care for older patients, and it predicts the likelihood that they will recommend their providers to others.