Complex regional pain syndrome (CRPS) is characterized by chronic spontaneous and/or evoked regional pain disproportionate in severity, distribution, and/or duration to that typically experienced after a similar injury or illness. The pain may also begin without a known precipitant. While various authors have questioned the validity of the diagnosis, physicians will be asked to perform impairment ratings on patients diagnosed with CRPS. Hence, it is important to understand the issues associated with this syndrome; the diagnostic criteria for it, including the need to rule out other diagnoses that may explain the patient's presentation; and how to rate CRPS. The AMA Guides to the Evaluation of Permanent Impairment, Fifth Edition, provides approaches to assessing CRPS impairment that are refined in the Sixth Edition.