In a retrospective study of 115 patients with giant cell arteritis, 5 clinically patent autoimmune diseases were recorded; including 2 patients (1.8%) with Grave's disease and 1 with hypothyroidism. Among these patients, 46 had systematic assays of blood thyroid hormones and 39 were systematically investigated for anti-thyroid antibodies (ATAb):3 (6.5%) had biological hypothyroidism and 4 (10.3%) had ATAb. These findings were not significantly different from those of a control group of 39 age and sex matched patients.