Adipsic diabetes insipidus (ADI) is a rare condition in which thirst, an essential clinical feature for the prevention of hypernatraemic dehydration, is absent. We report the first case of adipsic diabetes insipidus to occur following surgery for a pituitary macroprolactinoma, with loss of both osmoregulated and baroregulated vasopressin release. Following extensive surgery for a vision threatening macroprolactinoma a 14-year-old boy developed profound hypernatraemia with absent thirst sensation. Detailed investigation, with hypertonic saline infusion and trimetaphan infusion, revealed absence of both osmoregulatory and baroregulatory release of vasopressin. We discuss the investigation and management of such patients and the physiology of hypothalamic-neurohypophyseal dysfunction in such patients.