This is a retrospective review of vitamin D levels in patients with thyroid eye disease (TED). Vitamin D levels in 89 patients with Grave’s disease and TED were compared against 89 patients with Grave’s disease and no TED. They also compared both these groups against matched controls without Grave’s disease. They found that vitamin D levels were significantly lower in the TED group compared against the Grave’s disease without TED group and the controls. There was no significant difference between the Grave’s disease without TED and the controls. Low vitamin D is known to increase the risk of autoimmune disease, but this is the first study demonstrating a correlation between low vitamin D and TED. There is no single internationally recognised normal range for Vitamin D, but the levels in the TED group (24.8ng/ml +/-13.2ng/ml) would include patients which most clinicians would consider sub-normal. The main weaknesses of the study are that it is retrospective and that vitamin D levels were measured up to a year after the diagnosis of Grave’s disease or TED and may have been affected by supplements. Although no causative role has been proven, the significance level is high and the findings merit further investigation as treatment of vitamin D deficiency may have a role in the management of TED.