Pulsating exophthalmos may arise from: (1) arteriovenous aneurysms of the brain, orbit or cavernous sinus; (2) arterial and arteriovenous aneurysms of the orbit and (3) defective roof of the orbit. The treatment for pulsating exophthalmos, therefore, is dependent on and directed to the underlying cause. In the case here reported (fig. 1), the pulsating exophthalmos was due to an orbital meningocele of congenital origin. It would perhaps be more correct to speak of congenital absence of the roof of the orbit, for doubtless this defect was primary, the cerebral meningocele following in its wake as a necessary mechanical sequel. The differential diagnosis of the cause of the pulsating exophthalmos was based on the positive roentgenologic evidence that the roof of the orbit was in large part missing on the affected side (figs. 2 and 3). The explanation of the exophthalmos was that the unopposed pressure of the