Clinical and laboratory findings of 237 consecutive patients who had 250 temporal artery biopsies performed at the Wilmer Institute during a 15-year period were reviewed. Biopsies were reviewed independently on three separate occasions by four observers who, unaware of the clinical history, made one of the following histopathologic diagnoses: active arteritis, healed arteritis, arteriosclerosis, atherosclerosis, normal, or other. Biopsies were reviewed a fourth time by the observers together to establish a consensus diagnosis. The frequency of intraobserver disagreement in biopsy interpretation ranged from 4.4 to 25.6% of cases. The frequency with which observers disagreed with the consensus diagnosis (interobserver variation) ranged from 4.3 to 13.5% of cases. Pre-biopsy steroid therapy for seven to eight weeks or longer was associated with loss of the histopathologic features of active arteritis. We recommend biopsies for all patients with known contraindications to steroid therapy. In addition, multivariant regression analysis suggests that certain patients can be selected who are likely to have positive biopsies. For some patients, the clinical diagnosis of temporal arteritis can be based on the clinical signs and symptoms and their response to a therapeutic trial of steroids.