BACKGROUND: Idiopathic central diabetes insipidus (CDI) can be diagnosed when it occurs in the absence of a genetic or secondary cause known to be responsible for diabetes insipidus (DI). Some studies have reported that idiopathic CDI in adults shows a more benign clinical course than in children and young patients. However, the clinical characteristics and progress of this disorder have not been fully described. Therefore, we investigated the clinical courses of adult patients over the age of sixteen years with idiopathic central DI. METHODS: We reviewed the medical records of all patients who had documented cases of idiopathic CDI from 1989 to 2005, and studied clinical features, hormone data, and imaging studies at diagnosis and during at least 1-year of follow-up. RESULTS: There were 9 male (30.0%) and 21 female (70.0%) patients with a mean age of 39.3 years at diagnosis and a mean follow-up duration of 6.9 years. At diagnosis, deficits in anterior pituitary hormones were documented in 6 patients (20%), hyperprolactinemia in 4, and hypogonadism in 2. Two patients had an anterior pituitary hormone deficiency that was newly detected at a mean 3.4 years after the onset of DI. On initial MRI, the posterior pituitary was not hyperintense in 7 of the 30 patients (23.3%), but pituitary stalk thickening was observed in 15 (50.0%). After a mean follow-up of 6.9 years (range: 1 to 18), follow-up pituitary MRI showed improvement or no changes in patients with initial MRI findings of a pituitary abnormality, and no development of new lesions in 7 patients with a normal pituitary finding on initial MRI. CONCLUSION: Two of the 30 patients with idiopathic CDI developed an anterior pituitary hormone deficiency during follow-up, but no subject showed any aggravation on follow-up MRI. No patient showed a newly developed pituitary abnormality on follow-up MRI after a negative finding on the initial MRI.