The majority of cases of central diabetes insipidus are still pathogenetically unclear (idiopathic). Atherosclerotic cholesterol emboli might be partly responsible for some of these idiopathic cases. A 54-year-old woman with known aortic valve stenosis and a history of a transitory ischemic attack presented with sudden-onset polyuria and polydipsia of up to eight l/d, which had started acutely with headaches. She had been treated with lithium for 3 years because of cyclothymic depression. Plasma sodium was in the upper normal range (142-148 mmol/l). Hypertonic saline infusion during lithium therapy revealed a normal threshold of thirst and resetting of vasopressin secretion (osmotic threshold > 300 mosmol/l), whereas vasopressin reserve was normal. Lithium withdrawal led to an even greater delay of vasopressin release upon hypertonic saline infusion (> 310 mosmol/l). Pituitary function tests revealed a normal anterior pituitary function. MR imaging of the hypothalamo-hypophyseal region showed a normal hypothalamic region and a highly intensive neurohypophyseal signal in the T1-weighted image. The patient responded well to desmopressin. We suggest that in this rare case clinical symptoms as well as biochemical findings like impairment of AVP release might be related to a minor structural hypothalamic damage by a vascular lesion, caused, for example, by an atheromatous (cholesterol) embolism in the hypothalamic region responsible for integration of osmoreceptor function and AVP-secretion. The patient's atherosclerosis and aortic stenosis might be responsible for this event.