The incidence of medically recognized cluster headache within Olmsted County, Minnesota, from 1989 through 1990, was determined by using modified International Headache Society criteria. The results were compared with previously published incidence data from 1979 through 1981. The overall age- and sex-adjusted incidence decreased from 9.8/100,000 person-years in 1979-1981 to 2.07/100,000 person-years in 1989-1990.