Epidemiology of chronic daily headache.

Over the last 10 years an increasing amount of data regarding the prevalence of chronic daily headache (CDH) has been published. The economic implications of chronic daily headache have now grown in importance in view of the increasingly limited financial resources in the health care system. In addition to recording data regarding the prevalence of this disease, epidemiological studies have also dealt with analysing and evaluating the quality of life of the afflicted patients.