Epidemiology of migraine and tension-type headache.

The introduction of operational diagnostic criteria for the primary headaches in 1988 has provided new opportunities for comprehensive epidemiologic headache research. In recent years, several studies on the epidemiology of the primary headaches have emerged. This review deals with methodologic considerations and provides a "snapshot" of the main findings in these studies. The importance of epidemiologic studies in clarifying the natural history of the primary headaches, including the distinction between separate clinical entities, is elucidated.