Primary polydipsia is an eating disorder which is often sub-diagnosed particularly in psychotic patients. Through a clinical observation of a patient who was treated for schizophrenia since 28 years and has presented a primary polydipsia, we suggest discussing the diagnostic and the therapeutic difficulties of this disorder.

Mr D.R, 46 years old, followed up since the age of 18 for a schizophrenia and a mental retardation. Despite the important dose of classic neuroleptic treatment and different association of classic neuroleptics, we never noted an improvement of the psychotic symptoms. One year ago, he had been hospitalized in a reanimation department for a metabolic encephalopathy secondary to a severe hyponatremia due to a primary polydipsia.

The eating disorder associated with a psychotic illness doesn’t usually fill all the criteria of the DSM IV classification and is often classified as an eating disorder not otherwise specified. It's important to notice that the early beginning of schizophrenia is one of major risk factors of primary polydipsia. Besides, many other mechanisms are involved to explain primary polydipsia Psychotropic substances can lead polydipsia especially neuroleptics because of an inappropriate secretion of the ant diuretic hormone or by their anticholinergic effect by increasing oral drought. Clozapine remains the best indication because it permits the stabilization of psychotic signs and the decrease of primary polydipsia at the same time.

Primary polydipsia has to be diagnosed and treated at time in psychotic patients to avoid serious complications of hyponatremia which can be fatal.