PROLACTIN (PRL) LEVELS ARE frequently elevated in patients with non-PRL-secreting adenomas or other intrasellar and parasellar diseases (“pseudoprolactinomas”). This phenomenon is believed to result from a loss of dopaminergic inhibition on pituitary lactotrophs and is known as the “stalk-section effect.” Using magnetic resonance imaging scans and a high-magnification sella technique, we measured a number of parameters indicative of the disruption of normal sellar structures. The investigator was blind to the patient's diagnosis and PRL level while collecting the data. Parameters measured were the tumor size, the angular deviation of the pituitary stalk, and the degree of compression of the pituitary stalk. Measurements were obtained from 44 patients with pathologically confirmed tumors that had no immunohistochemical reactivity to PRL. PRL levels were often higher than expected. Four patients (9%) had a PRL level of more than 150 ng/ml, and three patients (7%) had a PRL level of 200 ng/ml or more. One patient with a plasmacytoma eroding the sella floor had a PRL level as high as 504 ng/ml. There was no significant correlation of PRL level and the degree of pituitary stalk compression, stalk deviation, or tumor size. PRL levels were found to be markedly elevated in some patients with a tumor causing little distortion of the pituitary stalk. Conversely, PRL levels were often normal despite evidence of massive distortion of the stalk. Therefore, magnetic resonance imaging evidence of pituitary stalk distortion cannot be used to determine the diagnosis of prolactinoma versus pseudoprolactinoma in most cases. The lack of correlation of PRL level in patients with nonprolactinomas is important in view of recent doubts concerning the role of the “stalk-section effect.” A number of illustrative cases are presented.