In the Vågå study of headache epidemiology, a search was made also for cluster headache. Of the available 18-65-year-old dalesmen, 1838 (88.6%) could be examined personally (O.S.) - 51.3% females and 48.7% males. Based on current International Headache Society criteria, cluster headache seemed to be present in seven dalesmen, one female and six males (corresponding to a total prevalence of 381 per 100 000; 95% confidence interval (CI) 153-783 per 100 000). Except for the female gender, the female case was fairly typical. In one case, there were short-lasting bouts ('minibouts'). It was felt that this also was a genuine case of cluster headache. If one excluded the latter case, there would be one female and five males [a prevalence of 106 per 100 000 for females, and 558 per 100 000 for males, giving a prevalence in the total population of 326 per 100 000 (95% CI 120-709 per 100 000)]. The confidence interval was considerable. This study therefore does not give a clear indication as to prevalence.