Psychogenic polydipsia and its frequent complication, water intoxication, are well-known to psychologists. There are biochemical and psychiatric theories of psychogenic polydipsia which often correlate with each other. A 48-year-old man with chronic paranoid schizophrenia developed symptoms of psychogenic polydipsia. This provoked disturbances in electrolyte balance, resulting in a rapid decrease in serum sodium concentration and eventual death. There is a paucity of information and little awareness of this problem in the professional literature.