Rating the impairment related to various chronic painful conditions, including headaches, is challenging and is addressed in the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides) in a section of the chapter on pain. Primary headache disorders include migraines, tension-type headaches, and cluster headaches caused by disturbances in the central nervous system. Headaches occur with varying intensities and frequencies but follow three broad patterns: 1) minimal, slight, moderate, and marked headache; 2) cycles or episodes that may last from moments to years; and 3) consistent and persistent pain that may last years, decades, or a lifetime. Physicians should estimate impairment related to headache pain according to the procedures discussed in section 15.8, including a multidimensional assessment of an individual's capabilities, including biological, psychological, and social aspects and excluding the existence of a separate comorbid pathologic process. The AMA Guides does not provide specific numeric values for impairment of headache or for pain itself. For patients who have a primary headache disorder, the physician should clearly understand the frequency and severity of the condition, the approach to treatment, and the effects of headaches on activities of daily living. The discussion of headaches in the AMA Guides emphasizes the importance of careful evaluation over merely assigning a numeric value to an impairment.