Purpose: There is much evidence suggesting that older adults are often negatively affected by aging stereotypes; however, no method to identify individual differences in vulnerability to these effects has yet been developed. The purpose of this study was to develop a reliable and valid questionnaire to measure individual differences in the tendency to anxiously expect, readily perceive, and intensely react to age-based rejection among older adults: the Age-Based Rejection Sensitivity Questionnaire (RSQ-Age). Design and Methods: A pilot sample of older adults was asked to identify situations in which negative outcomes related to being an older adult might occur. From these responses, 58 scenarios representing 8 domains and themes were identified. Thirty initial items were created from this pool of scenarios, and this 30-item RSQ-Age underwent intensive testing and refinement to create the final 15-item RSQ-Age. The 15-item RSQ-Age was assessed for internal and test-retest reliability, as well as construct validity. Results: Results revealed that the RSQ-Age has good internal (alpha = 0.91) and test-retest, r(72) = 0.74, p less than 0.01, reliability and is a valid measure of age-based rejection sensitivity (RS). Construct validity was supported by correlations with personal RS, age-based stigma consciousness, self-consciousness, awareness of ageism, and self-esteem. Implications: The RSQ-Age is a useful measure for researchers and health care workers interested in the relationships between expectancy, perceptions, and reactions to age-based stigma and subsequent cognitive, behavioral, and health-related consequences.