Global impact of Danish headache research.

Over the past 40 years, Denmark has established a world reputation for the comprehensive nature and excellence of its headache research. Advances have been made in epidemiology, genetics, pathophysiology and treatment across the whole spectrum of headache entities. Moreover, the IHS classification of headache, the guidelines for clinical trials and text books on the basic mechanisms and management of headaches were initiated from Denmark. These achievements are a tribute to all those who have participated and to the continuing leadership of Jes Olesen.