The author asks some questions that he estimates indispensable before any hospitalization, by reason of the concept less precise of "necessity of hospitalization". What is the disturbance and what will we observe or treat? What is the type of institution best adapted? Is it the patient that ones wants to relieve first, and not the milieu? He then reviews the different categories of patients met in the psychiatric services, by reconstituting the channel who brought them and by redeeming the behavior notion of crisis reaction from the patient in his environment. He concludes that the psychiatric hospitalization, responding at a momentary necessity of the history of the subject, cannot constitute the center of a therapeutic system and that the hospital is only a tool among others.