A follow-up study of 29 patients with giant cell arteritis (GCA) was undertaken to determine the duration of corticosteroid treatment. In 20 patients the diagnosis was confirmed by biopsy of a temporal artery (Group 1). In 9 patients GCA was evident clinically (Group 2). Treatment was continued until reductions in corticosteroid dosage no longer resulted in clinical evidence of GCA. The mean duration of corticosteroid treatment was 6 yr. The diagnosis of GCA should be confirmed by means of a temporal artery biopsy before treatment is begun because it may commit the patient to years of corticosteroid treatment.