TEN PATIENTS WITH OPTIC NERVE INVOLVEMENT associated with thyroid dysfunction are reported in this study. This is the largest group reported from any one institution. Such optic nerve disease is relatively uncommon and most reports in the literature are limited to one or two cases. However, two series of six patients' 2 and one of four3 have been published in sufficient detail within recent years to be of value for comparison. Each patient had orbital changes characteristic of those associated with Graves' disease. These consisted of tearing and irritation of the eyes, as well as upper lid retraction, deep injection at the outer aspects of the globes, lid swelling, chemosis, and extraocular muscle involvement. All these signs were not present in every patient, but the clinical picture in each case suggested the correct diagnosis. Only one patient showed any corneal irregularity, and this was slight. The fundi were examined with dilated pupils to eliminate other causes for the visual disturbances. In each instance the ocular tension was normal. Papilledema or papillitis offered little difficulty in diagnosis, but retrobulbar optic nerve involvement was diagnosed only in the presence of consistent visual field defects. CASE REPORTS CASE 1 A 59-year-old white male who was treated for byperthyroidism with R.A.I. in December, 1957. One year later his lids became puffy, the eyes felt sandy, and he had double vision on upward gaze. When first seen on April 7, 1959, the lids were full, the lacrimal glands palpable, the upper lids retracted, both globes showed deep injection temporally and there was marked limitation of elevation as well as of lateral movement.