OBJECTIVE Exophthalmos was noted in 4 of the 12 patients reported by Harvey Cushing in 1932. Although exophthalmos has often been included in clinical descriptions, no previous study has reported actual measurements in patients with active and treated Cushing's syndrome, and in control patients. The aim of this study was to obtain these measurements.PATIENTS Thirty‐one patients with active Cushing's syndrome (19 iatrogenic), 15 with treated Cushing's syndrome, 18 with Graves' ophthalmopathy, 59 control patients, and 3 patients with active Cushing's syndrome plus a family or personal history of thyroid disease.DESIGN AND MEASUREMENTS A consecutive series of patients with active and treated Cushing's syndrome were assessed. They were compared with patients with Graves' ophthalmopathy, and with control patients. Exophthalmos was assessed by the author using a Hertel meter. Urinary free cortisol was measured on patients with Cushing's syndrome, and serum thyroxine was estimated for them, and for the patients with Graves' ophthalmopathy.RESULTS Exophthalmos exceeding 16 mm (>2 SD above normal mean) was found in 45% of active Cushing's syndrome, 21% of iatrogenic Cushing's syndrome, 20% of treated Cushing's syndrome, 2% of normal controls, and 77% of patients with Graves' ophthalmopathy. No patient with Cushing's syndrome had significant symptoms due to exophthalmos.CONCLUSION Patients with active Cushing's syndrome have statistically significant exophthalmos. This rarely causes symptoms, and diminishes when cortisol concentrations become normal. Cushing's syndrome and autoimmune thyroid disease may coexist in patients wi