Table 1 Previous epidemiological studies on the incidence or prevalence of cluster headache.

Study	Country	Results
This study	Germany	0.15% (12 month prevalence)
Ekbom et al 20066	Sweden	0.15% (lifetime prevalence)
Torelli et al 20054	Italy	0.28% (lifetime prevalence)
Sjaastad and Bakketeig 20033	Norway	0.38% (lifetime prevalence)
Tonon et al 20022	San Marino/Italy	0.056% (lifetime prevalence)