ALTHOUGH the association of exophthalmos with goiter was recognized as early as the twelfth century (1), the modern focus on the constellation of hyperthyroidism, diffuse goiter, and endocrine ophthalmopathy is best attributed to the work of Caleb Parry (1825) (2), Robert Graves (1835) (3), and Carl von Basedow (1840) (4). Since their early descriptions a plethora of reports have been published detailing the clinical and histologic features of endocrine ophthalmopathy and coining a variety of colorful synonyms and eponyms (5, 6). There remained, however, a number of important unanswered questions. These deal with the nature of the inciting factor, the pathogenesis of the disease, the unique and often asymmetric involvement of extraocular muscles, the relationship between the eye disease and the thyroid abnormality, and the most rational and efficacious methods of treatment. We will review the clinical, anatomic, histologic, and immunologic features of endocrine ophthalmopathy particularly as they apply to these issues.