Unilateral exophthalmos is not of necessity similar etiologically to the bilateral condition. There is no doubt that many unilateral exophthalmic conditions may be simply incomplete, in terms of bilateral involvement seen in cases of exophthalmic goiter. It is just as true, however, that in many cases the primary characteristic is unilateral displacement of the eyeball. Involvement of the opposite side would be in such cases secondary and not consequent. Perhaps the best example of such instances is a case of neurofibromatosis. It seems as though unilateral exophthalmos is properly considered a definite clinical entity in a large number of instances. Even in cases of unilateral exophthalmos associated with exophthalmic goiter this condition, in my experience, presents various signs less commonly seen in cases of the bilateral variety. There is no certain reason why exophthalmos should at times be almost purely unilateral, but the fact stands that