Thyroid-associated ophthalmopathy (TAO) is one of the most vexing problems in endocrinology but its relationship to thyroid autoimmunity is becoming more clear with the realisation that almost all patients with Graves' disease have this condition and almost all patients with ophthalmopathy have some form of thyroid involvement. This suggests cross reactivity between thyroid and retrobulbar antigens, of which one potential candidate has recently been cloned. Together with new information on predisposing factors and the important role of the retrobulbar fibroblasts, these developments shed new light on the aetiology and pathogenesis of this enigmatic disorder.