Workers’ compensation jurisdictions use the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides), in various ways, including as a proxy for disability, either as a direct correlate or as a threshold indicator. The AMA Guides clearly states that it should not be used for direct estimates of work ability: “it is inappropriate to use the Guides’ criteria or rating to make direct estimates of work disability.” The Maine Supreme Court ruled on two cases in which the resolution depended on the critical question of what impairment was being rated—that due to the injury or to all impairment. The court found that statutory language regarding personal injury may include a pre-existing condition when the work injury aggravates, accelerates, or combines with the pre-existing condition in a significant manner. The Commonwealth of Pennsylvania also uses impairment as a threshold to determine if an employee is totally disabled: Act 57 requires employees who have received total disability benefits for 104 weeks to submit to an impairment rating evaluation. The actions in both states raise questions about the reasonableness of using impairment to determine disability: What is the average extent of impairment among the working population? How can multisystem impairment be rated effectively? Few physicians have been trained in the use of the AMA Guides, and fewer understand the complexities of multisystem rating.