This study presents preliminary validation data on both the Acceptance and Action Questionnaire—Acquired Brain Injury (AAQ-ABI) and the Acceptance and Action Questionnaire—II (AAQ-II). Data from 150 participants with ABI was subject to exploratory factor analysis on the AAQ-ABI (15 items). A subset of 75 participants with ABI completed a larger battery of measures to test construct validity for the AAQ-ABI and to undertake a confirmatory factor analysis (CFA) on the AAQ-II (7 items). Three meaningful factors were identified on the AAQ-ABI: Reactive Avoidance, Denial, and Active Acceptance. Reactive Avoidance demonstrated good internal and test–retest consistency (α = .89) and correlated in expected directions with other related measures including the AAQ-II. CFA of the AAQ-II did not provide a good fit but did have similar correlations with measures of psychological distress as found in prior non-ABI samples. The results suggest both measures can be used with individuals following an ABI but they index different facets of psychological flexibility. The AAQ-ABI appears to measure psychological flexibility about the thoughts and feelings relating to the brain injury itself while the AAQ-II measures psychological flexibility around general psychological distress. Future research could explore the additional 2 factors of the AAQ-ABI and use these measures in outcome studies that promote psychological flexibility in individuals with an ABI.