The assessment of impairment due to alteration in mental status, cognition, and highest integrative function may be challenging. A review of impairment assessments performed by others can provide valuable insights, including an appreciation of how evaluators may misapply the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides), Sixth Edition. As a teaching example, this article presents an erroneous rating for a claim of cognitive impairment. The authors point out that most of the misdirection in the case example could be identified with reference to the AMA Guides, Sixth Edition, which reveals discrepancies between the rating processes in this case and actual sixth edition methodology. Nevertheless, the case example involved certain components that were so unconventional that it would have been impossible for the sixth edition contributors to anticipate the need to write a text that would have prevented these errors. The process of sorting out this misdirected rating revealed a previously unanticipated need to clarify sixth edition methodology, and the present article provides such clarification. The concluding section of this article provides a step-by-step protocol for the AMA Guides, Sixth Edition, methodology that involves rating cognitive impairment using Section 13.3d, Mental Status, Cognition, and Highest Integrative Function. The fourteen steps outline a meticulous process based on appropriate clinical assessment, application of evidence-based medicine, and the process outlined in the AMA Guides, Sixth Edition.