Graves' ophthalmopathy (GO) remains one of the most enigmatic and difficult conditions an endocrinologist sees. Despite considerable study, we still do not know why some Graves' patients run into major, vision threatening problems and others do not; similarly, we do not know the link between the thyroid and the eye and how GO can be asymmetrical. On the other hand, previously obscure intraorbital autoimmune responses are gradually being illuminated by modern investigative techniques, and we now recognise that the proximal cause of GO is activation of fibroblasts within the extraocular muscles, most probably due to cytokines released by infiltrating lymphocytes [1,2]. Immunologically, what remains elusive is the identity of the auto-antigen to which these T cells are responding: this brief review will summarise recent progress.