Chapter 18, Pain, is the first attempt in the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides), Fifth Edition, to define comprehensive pain evaluation and rating. Chapter 18 focuses on situations in which the pain itself is a major cause of suffering, dysfunction, or medical intervention even though an examining physician can find no demonstrable active disease or autonomic changes. These statements likely would be rejected by rating systems that require a physiologic basis for rating. Other chapters in the AMA Guides typically account for pain as part of specific impairment ratings; for example, a physician who rates cervical spine impairment must decide if a rating for pain beyond the original rating is appropriate. Many rating systems would reject such a rating for pain because of its subjective nature, but, despite these difficulties, even restrictive rating systems may require the use of Chapter 18 because, according to the AMA Guides, no other available method exists for considering impairment of certain conditions such as postherpetic neuralgias or migraines. As the AMA Guides acknowledges, Chapter 18 seems to allow impairment ratings caused by pain and suffering but at the same time to forestall actually assigning a number. One hopes for refinements in our understanding of chronic pain treatment and outcomes; in the interim, knowledgeable raters should guide nonmedical personnel toward a reasonable understanding of this chapter.