Eye disease was associated with hyperthyroidism in 202 of 221 patients with active Graves' ophthalmopathy (91.4%) and was not accompanied by thyroid hyperfunction (euthyroid Graves' disease) in the remaining 19 (8.6%). All the latter patients had some mild thyroid abnormalities (thyroid autoantibodies, negative TRH test, negative T3 suppression test, goitre). Sex distribution analysis evidenced a higher prevalence in females with a female/male ratio of 2.1 which was, however, significantly lower (P less than 0.05) than that observed in control (Graves' disease patients without overt ophthalmopathy (female/male ratio = 3.4]. Patients with euthyroid Graves' disease showed a female/male ratio of 0.7. Age distribution revealed a peak prevalence in the 5th decade of life, identical to that of Graves' disease without ophthalmopathy. A close temporal relationship between the onset of hyperthyroidism and the onset of ophthalmopathy was found, since in about 85% of the patients the first ocular manifestations occurred within +/-18 months around the onset of hyperthyroidism.