Protrusion of the eyes of patients with autoimmune thyroid disease was compared with that of healthy subjects. The mean values for protrusion in patients with thyrotoxic Graves' disease and Hashimoto's disease and in healthy subjects were 16.6 +/- 2.1 mm (mean +/- SD; n = 122), 14.2 +/- 1.8 mm (n = 100), and 13.9 +/- 1.9 mm (n = 558), respectively. The value of Graves' disease was significantly different from that for healthy subjects (P < 0.001). Individual values for protrusion showed a similar normal distribution in these three groups, but were displaced to higher values as a whole in Graves' disease. These results, which suggest that almost all patients with Graves' disease have exophthalmos, do not support the idea that Graves' ophthalmopathy is a distinct single autoimmune disease.