Objective: To validate the use of the Abbreviated Westmead Post-traumatic Amnesia Scale (A-WPTAS) in the assessment of acute cognitive impairment in mild traumatic brain injury (mTBI). Methods: Data previously collected from 82 mTBI and 88 control participants using the Revised Westmead Post-traumatic Amnesia Scale (R-WPTAS) was converted to A-WPTAS scores and pass/fail classifications were calculated for both scales. Results: The proportion of failures on the R-WPTAS and the A-WPTAS did not differ and a similar number of mTBIs were classified on each. For mTBIs the relationship between the independent memory test and a pass/fail classification was the same for both scales. Bivariate logistic regressions revealed that mTBIs, relative to controls, were around 8 times more likely to fail the assessment (R-WPTAS: 95% CI: 3.7018.87; A-WPTAS: 95% CI: 3.7020.14). As verbal learning improved the likelihood of failure was reduced. Greater education was associated with a decreased likelihood of failure. The relationship between education and a fail performance was not sustained when education was adjusted for the effect of age, prior mTBI, blood alcohol level, injury status, verbal learning, and morphine administration. Conclusions: The A-WPTAS is a valid measure. The A-WPTAS may reduce the risk of failing to classify patients with mTBI by identifying and documenting acute cognitive impairment.