Purpose: To assess the lacrimal glands in patients with thyroid eye disease with diffusion-weighted magnetic resonance (MR) imaging. Material and methods: This study was carried out on 44 consecutive patients (17 males, 27 females, with mean age 36 years) with thyroid eye disease and 20 age-and sex-matched volunteers. They underwent diffusion-weighted MR imaging of the orbit. The apparent diffusion coefficient (ADC) values of the lacrimal glands were calculated and correlated with the clinical activity score (CAS). Results: The mean ADC of lacrimal glands in thyroid eye disease (1.73 × 10-3 mm 2 /s) was significantly higher (p = 0.001) than that of volunteers (1.52 × 10-3 mm 2 /s). The cutoff ADC value of lacrimal gland used for differentiation of thyroid eye disease from volunteers was 1.62 × 10-3 mm 2 /s with an area under the curve value of 0.95 and an accuracy of 96%. There was significant difference (p = 0.03) in the ADC of the lacrimal glands in patients with active (n = 24) and inactive (n = 20) disease. The cutoff ADC value of the lacrimal gland used to suspect active disease was 1.76 × 10-3 mm 2 /s with an area under the curve value of 0.80 and an accuracy of 82%. There was positive correlation between the ADC value of the lacrimal glands and CAS (r = 0.73, p = 0.001). Conclusions: The ADC of the lacrimal glands is a non-invasive imaging parameter that can be used for diagnosis of thyroid eye disease and to predict the active form of the disease.