T1-weighted magnetic resonance (MR) images of the pituitary gland and sella turcica routinely demonstrate a region of high signal intensity in the neurohypophysis. High-resolution MR imaging studies of the sella turcica in 200 subjects with a normal or abnormal sella were analyzed. The hyperintensity was found in the images of about 90% of healthy subjects and patients with microadenoma, in only 43% of patients with macroadenoma, and in 12% of patients with empty sellae. The signal was absent in several patients with functional or anatomic abnormalities of the hypothalamic-hypophyseal axis. It is concluded that the high signal intensity in the posterior lobe of the pituitary gland is present in most healthy individuals and that its absence in many patients with large intrasellar masses and empty sellae is due to compression of posterior lobe tissue. Its absence in diabetes insipidus further suggests a relationship between hyperintensity and the functional status of the hypothalamic-hypophyseal axis.