Computed tomography (CT) is the procedure of choice for initial evaluation of patients suspected of having chiasmal or perichiasmal lesions. Over 1000 patients were examined with high resolution CT, using axial and coronal scans, contrast enhancement, multiplanar reformations, and, when indicated, metrizamide CT cisternography. The normal anatomic appearance of the chiasm and neighboring structures is demonstrated, as are various pathologic conditions. CT criteria suggesting chiasmal disease are: (1) symmetric or asymmetric enlargement of the chiasm; (2) areas of abnormal density, without or with contrast enhancement, in the chiasm or perichiasmal region; (3) alteration of the suprasellar cistern; and (4) distortion of the anterior-inferior third ventricle. © 1983.