Measurement of the optic nerve diameter by echographic technique has been performed in 40 patients with intracranial hypertension syndromes of various origin. In all the cases examined the diameter was always increased. Postoperative checks revealed a decrease of the nerve thickness until it reached the normal values. The changes in the optic nerve diameter reflect the variations of the intracranial pressure and they appear earlier than any changes in the fundus oculi. This simple and non-invasive echographic technique is very useful in following patients with an intracranial hypertension syndrome.