We investigated the role of MR imaging for evaluation of the functional status of the neurohypophyseal system in both idiopathic central diabetes insipidus (DI) and familial autosomal dominant neurohypophyseal DI. The patients and family with DI were analyzed retrospectively for the presence or absence of posterior pituitary gland hyperintense signal on MR images. A total of 19 adult patients with idiopathic central DI, 7 members of a family with autosomal dominant DI and 20 control subjects were included in the study. Diagnosis of idiopathic DI was based on the presence of central DI in the absence of any alteration that is known to be responsible for DI. The patients were studied retrospectively and the morphology and intensity of the posterior lobe by MR imaging was assessed by blinded reading. In all patients with idiopathic central DI and the affected members of the family, the posterior bright signal was absent while the stalk was normal on MR images. In contrast, normal posterior pituitary bright signal and stalk were found in unaffected members of the family and all control subjects. We conclude that MR imaging of the posterior pituitary lobe can be used to evaluate the functional status of the neurohypophyseal system in idiopathic central DI and familial autosomal dominant DI.