This article reviews portions of the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides) that are useful to evaluators making individual case decisions in various legal systems. The first step is a determination of permanency, and evaluators should know that many state laws have unique definitions of “maximum medical improvement.” Next, the evaluator should establish a definitive diagnosis that identifies the existence of an abnormality and impairment of the activities of daily living. Based on his or her judgment and expertise, training, skill, and thoroughness, the evaluating physician must use clinical judgment regarding whether or not the results of tests or impairment measurements are reasonable for a particular patient and the impairment under evaluation. The AMA Guides notes that an evaluator may increase an impairment rating after determining that the estimate for the anatomic impairment does not sufficiently reflect the severity of the patient's condition. When findings between two physicians differ, then the stability of the medical issue may be in question, and the involved physicians should be in communication and should have access to all prior physician reports and test results. Evaluators may need to educate patients about the difference between impairment and disability. Clear report writing is the key to successful impairment evaluations.