It is likely that the symptom of headache confronts the general practitioner more frequently than any other. It is something that often carries with it mental anxiety as well as physical discomfort because it contains an element of fear coupled with an "inescapable" type of pain. It is found as part of many conditions, functional as well as organic, but unless its cause is obvious it is passed over by the physician, and other symptoms, often less annoying to the patient, are given chief attention and treatment. Only in recent years have headaches been classified clearly as to cause and their mechanisms clarified by Wolff's brilliant observations.1 We feel that a discussion of these mechanisms and causes of headache will give a working clinical classification which will clarify this common and disabling symptom. The purely basic and mechanistic classification of Wolff seems too broad, while Horton's2is too