Chronic daily headache (CDH) refers to a broad range of headache disorders occurring greater than 15 days a month — in many cases daily — for a period of at least 3 months. The primary variety of chronic daily headache is further subdivided into two distinct categories: headaches lasting more than 4 hours and headaches lasting less than 4 hours. There may be as many as 5% of the population encountering severe headaches on a daily or near-daily basis, and these individuals make up the majority of consultations to specialists.