We describe a 30 year old man who developed chronic adipsic hypernatraemia and hypothermia following a subarachnoid haemorrhage from an anterior communicating artery aneurysm. Anterior pituitary function tests were normal. Hypothermia was demonstrated over 4 years with loss of the ability to control heat conservation despite body temperatures as low as 30 degrees C. He failed to experience thirst despite plasma sodium concentrations of up to 187 nmol/l and plasma osmolalities of up to 397 mOsm/kg. The slope of the plasma vasopressin-plasma osmolality curve indicated loss of the osmoreceptor. There was an absent vasopressin response to insulin-induced hypoglycaemia but a normal response to apomorphine. The apomorphine-stimulated immunoreactive vasopressin was shown to behave identically to the synthetic peptide on HPLC and was bioactive.