Objective: Intraindividual variability (IIV)—variance in an individual’s cognitive performance—may be associated with subsequent cognitive decline and/or conversion to dementia in older adults. This novel measure of cognition encompasses two main operationalizations: inconsistency (IIV-I) and dispersion (IIV-D), referring to variance within or across tasks, respectively. Each operationalization can also be measured with or without covariates. This meta-analytic study explores the association between IIV and subsequent cognitive outcomes regardless of operational definition and measurement approach. Method: Longitudinal studies (N = 13) that have examined IIV in association with later cognitive decline and/or conversation to MCI/dementia were analyzed. The effect of IIV operationalization was explored. Additional subgroup analysis of measurement approaches could not be examined due to the limited number of appropriate studies available for inclusion. Results: Meta-analytic estimates suggest IIV is associated with subsequent cognitive decline and/or conversion to MCI/dementia (r = .20, 95% CI [.09, .31]) with no significant difference between the two operationalisations observed (Q = 3.41, p = .065). Conclusion: Cognitive IIV, including both IIV-I and IIV-D operationalizations, appears to be associated with subsequent cognitive decline and/or dementia and may offer a novel indicator of incipient dementia in both clinical and research settings. (PsycInfo Database Record (c) 2021 APA, all rights reserved)