PURPOSE: To compare tear film osmolarity between patients with thyroid ophthalmopathy and normal healthy subjects. METHODS: The tear film osmolarity in 15 normal subjects (15 eyes) (control group) and 21 patients (21 eyes) with thyroid ophthalmopathy was evaluated. Tear film osmolarity in milliosmole (mOsm) was determined by using an auto-osmometer. The palpebral fissure width, degree of proptosis, and tear break-up time (BUT) were also determined. The results for the two groups were compared statistically. RESULTS: The mean palpebral fissure width was 9.13 +/- 0.74 mm in the healthy subjects and 13.33 +/- 1.55 mm in the thyroid ophthalmopathy patients. This difference was statistically significant (P = 0.0001). The mean proptosis was 15.33 +/- 1.39 Hertel units in the healthy subjects and 20.71 +/- 0.95 Hertel units in the patients. This difference was also statistically significant (P = 0.0001). The mean tear BUT was 6.35 +/- 1.56 s in the patients and 18.27 +/- 1.53 s in the healthy subjects, and this difference was also statistically significant (P = 0.0005). The mean tear film osmolarity was 290.80 +/- 13.58 mOsm in the healthy subjects and 340.38 +/- 18.74 mOsm in the patients. There was a statistically significant difference between the groups (P = 0.0001). CONCLUSIONS: The significantly higher tear film osmolarity in patients with thyroid ophthalmopathy was most likely due to the increased proptosis and lid fissure width. These conditions may lead to injury of the ocular surface.