In the AMA Guides to the Evaluation of Permanent Impairment, (AMA Guides), Fifth Edition, two chapters claim relevance for pain complaints that lack an objectively demonstrable general medical basis: Chapter 14, Mental and Behavioral Disorders, and Chapter 18, Pain. Parts 1 and 2 of this four-part series examined forms of mental illness that commonly invoke complaints of pain; Part 2 also evaluations using the mental/behavioral chapter vs the pain chapter, and Part 3 noted the self-negating nature of the pain chapter's rationale (ie, the pain chapter presents a rationale that, taken literally, indicates it should not be used). A detailed case example illustrates how the decision about using the mental/behavioral chapter or the pain chapter often can be clarified by simply performing a thorough clinical evaluation (see Part 2 of this series). Examiners should be aware of the role of thoughts, behavior, and environmental contingencies on presentations of chronic pain even when no scientifically credible and objective general medical findings explain the pain. For example, the AMA Guides points out that in as much as 85% of low back pain cases, no explanatory physical pathology can be identified; therefore, readers are encouraged to be mindful of the professional literature. The authors of this series deny any attempt to move all instances of chronic pain into the category of mental illness but report little reason not to do so.