Ageism has been shown to have a negative impact on older people's health and wellbeing. Though multiple scales are currently being used to measure this increasingly important issue, syntheses of the psychometric properties of these scales are unavailable. This means that existing estimates of ageism prevalence may not be accurate. We conducted a systematic review aimed at identifying available ageism scales and evaluating their scope and psychometric properties. A comprehensive search strategy was used across fourteen different databases, including PubMed and CINAHL. Independent reviewers extracted data and appraised risk of bias following the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) guidelines. Of the 29,664 records identified, 106 studies, assessing 11 explicit scales of ageism, were eligible for inclusion. Only one scale, the 'Expectations Regarding Aging' met minimum requirements for psychometric validation (i.e., adequate content validity, structural validity and internal consistency). Still, this scale only assesses the 'stereotype' dimension of ageism, thus failing to evaluate the other two ageism dimensions (prejudice and discrimination). This paper highlights the need to develop and validate a scale that accounts for the multidimensional nature of ageism. Having a scale that can accurately measure ageism prevalence is key in a time of increasing and rapid population ageing, where the magnitude of this phenomenon may be increasing.