The Eastern Townships (Estrie) is an area of Québec which has never had a psychiatric hospital and is thus an extreme example of deinstitutionalization. How can people with the most severe mental illnesses be cared for? Does this system have harmful consequences? The authors present a case study with both qualitative and quantitative data to elucidate their questions. They found 36 patients with very severe mental illness (prevalence 12,4/100 000). This region does not send its most severely ill patients outside and generally succeeds in providing them with care and services in a network of small and medium size residential facilities. On the other hand, the authors have also been able to identify a certain drift of patients towards the correctional system ; cases with double or triple diagnosis do not easily have access to care ; through lack of an alternative, patients with potentially chronic violence often are stuck in a hospital in short stay beds (prevalence 1,6/100 000). It thus appears possible to eliminate the use of a psychiatric hospital for patients with very severe mental disorders as long as they are provided with supervised and long term care facilities (need : 10-20 places/100 000).