The IHS classification now divides TTH into subcategories, believed to be varieties of the same disorder. Individual attacks in infrequent episodic, frequent episodic, and chronic tension-type headache (ETTH) and (CTTH) have similar clinical features (1), although the severity of pain increases with frequency. Accordingly, CTTH is not only more frequent but also more severe (3,4). ETTH and CTTH forms are formally distinguished by their frequency of days with headache. Categorizing these subforms was originally based on practical more than pathophysiologic arguments; CTTH constitutes a large group of patients presenting to headache clinics and specialist practices, whereas patients with frequent ETTH are rarely seen by specialists or consult their general practitioners. Patients with infrequent ETTH essentially never consult a doctor for the problem. Further, patients with CTTH requiring prophylactic treatment often respond poorly to acute treatment, overuse medications, and have special management problems. A number of other special management problems are common in the chronic group. In more recent times, pathophysiologic and genetic-epidemiologic differences have been added to the practical reasons for a subcategorization.