The syndrome of an enlarged sella turcica with no intrasellar mass lesion but with an extension of a relatively large subarachnoid space into the sella is described. The frequency and mechanism of this entity is not certain, but in view of its occurrence, it would be advisable to study the contents of the sella turcica by means of pneumoencephalography prior to any definitive therapy of a patient with an enlarged sella turcica and pituitary dysfunction.