This article concludes the three-part discussion of differences among the editions of the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides): Third Edition Revised, Fourth, and Fifth Editions. The discussion begins with a comparison of different editions of the AMA Guides for evaluating lower extremity impairment and spinal impairment. The AMA Guides, Fourth Edition, introduced the Diagnosis related estimates (DRE) model, and in this edition the range-of-motion (ROM) model has only a limited role (ie, primarily as a differentiator). A table summarizes the criteria of spinal impairment criteria by edition of the AMA Guides. The authors summarize differences in the impairment ratings of various body systems based on the use of different editions of the AMA Guides, including differences in ratings of the cardiovascular, pulmonary, digestive, and other systems. Critiquing the AMA Guides, the authors call for improvements, including the following: add a system to rate permanent impairments, including functional limitations; base impairment ratings on scientific evidence and a valid whole person impairment scale; make the AMA Guides reliable, comprehensive, internally consistent, comprehensible, accessible (ie, the AMA Guides are complex and difficult to use, and not all physicians are capable of rating impairment), and acceptable. Despite the shortcomings, no other widely accepted basis to assess impairment is available, and future editions of the AMA Guides will improve the process of providing fair assessments of functional loss.