This article is part three of a four-part series that examines the rating of pain complaints and mental illness using the AMA Guides to the Evaluation of Permanent Impairment, (AMA Guides). Chapter 18 provides physicians with a method for evaluating impairment associated with “chronic pain states” for which there may be “no demonstrable active disease or unhealed injury,” and Chapter 14 should be considered when symptoms are out of proportion to physical findings. This article focuses on the directions from Chapter 18 and other pain resources. The authors note that Chapter 18 specifically addresses the issue of distinguishing between uses of Chapters 18 and 14, but the directions are contradictory with respect to the key question, Do “psychological factors” play a “major role” in the presentation of pain? Resources such as Bonica's Management of Pain point out that “[t]issue damage and nociception are neither necessary nor sufficient for pain,” suggesting that psychological factors are nearly always present and obviating the use of Chapter 18. A potential solution would be to ask, “Is the presentation of pain consistent with any mental illness as defined in the American Psychiatric Association's Diagnostic and Statistical Manual?” The decision rule then would be if the presentation of pain is consistent with any mental illness, then the mental and behavior chapter should be used.