Among the population of Olmsted County, Minnesota, 42 patients with temporal arteritis were identified during a 25-year period. The average annual incidence per 100 000 population aged 50 and older rose from 5.1 in 1950-1959 to 17.4 in 1970-1974. The prevalence of patients with a history of the diagnosis of temporal arteritis on 1 January 1975 was 133 per 100 000 population aged 50 and older. All patients received corticosteroid therapy for a range of 1 to 77 months (median, 7 months). Relapses in 10 of 11 patients were associated with corticosteroid reduction. The majority of patients recovered fully and were followed off corticosteroids for 10 months to 19 years (median, 5 years). Temporal arteritis had no significant effect on survival. Vertebral compression fractures and myopathy were the most serious complications of therapy. The presence of giant cells in biopsies was in part related to the number of sections examined, and their presence had no apparent influence on the clinical course.