The Sella Turcica has been one of the most studied and analyzed structures of the human body since the birth of radiology. Whether a sella is normal or enlarged has always been a challenge to radiologists, mainly because of anatomic variations and the wide range of “normal” measurements given by different authors. Attempts to correlate the size of the sella with the size of the head were made as early as 1917 by Fitzgerald (5) and by Gordon and Bell (6, 7) in 1922 and 1936. The variability of the anteroposterior and vertical diameters of the sella encouraged radiologists to evaluate other diameters and to propose technics to evaluate its area and volume (1, 4, 7, 11). The utilization of new positions and better radiographic equipment and technics brought new “signs” of abnormality of the sella that were incorporated in the radiological literature. Most of these signs were of the most interest in cases where the anteroposterior and vertical diameters of the sella were within normal limits. As Taveras and Wood (10) state, the size of the sella varies widely from individual to individual and there is a wide range of “normal.” They give 17 mm as top limit for the anteroposterior diameter, using the greatest anteroposterior diameter of the pituitary fossa. This measurement is taken from the most anterior to the most posterior margin of the pituitary fossa. The purpose of this paper is to demonstrate that there is a constant ratio between the anteroposterior diameter of the skull and the anteroposterior diameter of the sella, and that when this ratio is above “normal” the presence of an intrasellar expanding lesion should be considered, even in the absence of other radiological evidence of abnormality. These observations have been confirmed in adult skulls, and our main purpose is to disclose the value of this method in the early radiological diagnosis of pituitary adenomas. It is probable that other intrasellar expanding lesions will produce the same result. Method of Study Two hundred control subjects, all adults of both sexes, were studied. In all skull series had been obtained for different reasons and in none was an intrasellar adenoma or an intracranial mass suspected. The anteroposterior diameter of the skull and that of the sella turcica were measured in each case. The anteroposterior diameter of the sella was measured as proposed by Di Chiro and Nelson (4), that is, using the longest anteroposterior diameter in a horizontal plane. The anteroposterior diameter of the skull was measured as the maximum length between the inner table of the frontal bone and the inner table of the occipital bone (Fig. 1).