A better understanding of the clinical nature of Graves' orbitopathy will aid in the treatment of the disease as well as help to form a basis for clinical and pathophysiologic investigations. We studied the clinical data of 557 consecutive patients who were referred for treatment of Graves' orbitopathy. Clinical indexes were calculated based on ophthalmologic variables measured, grouped in the following categories: soft tissue, proptosis, muscle limitation, increase in intraocular pressure on upgaze, corneal staining, and visual acuity. The mean age at onset of orbital disease was 43.9 years for men and 44.4 years for women, an average of 2.5 years from the onset of thyroid disease. The male-female ratio was 0.29 in all age groups. Women were more likely to present with orbitopathy and hypothyroidism than were men (20% vs 11%) and less likely to be euthyroid (16% vs 34%, P < .01). Patients older than 50 years, compared with their younger counterparts, more often had symptoms of impaired ocular motility (32% vs 12%), signs of soft-tissue involvement (77.5% vs 68.6%), asymmetric soft-tissue involvement (15.6% vs 7.8%), more limited upward duction (22.2 degrees vs 29.4 degrees), and more impaired LogMAR visual acuity (0.092 vs 0.047, P < .01). Men had more limited upward duction than women (24.6 degrees vs 27.1 degrees) and greater increases in intraocular pressure on upgaze (7.80 mm Hg vs 5.78 mm Hg, P < .001). These data show thyroid orbitopathy to be a disease most common in younger women, but more severe, by most indexes, in men and patients older than 50 years. These groups of patients are also more likely to have asymmetric or euthyroid disease.