40 % of the homeless in Montreal suffer from severe mental disorder. Most of the time, deinstitutionalization is pointed out as the main cause of this situation. In fact, a closer survey of the problem proves there are much more complex causes to it than this only explanation. As a matter of fact, the modification of the law in order to take into account the rights and autonomy of the mentally ill patients is to be considered as one of the possible factors leading to homelessness because of the risk of health care interruptions. However, clinical commitment along with legal interventions and humanitarian interference could reduce the risk of homelessness and offer the most vulnerable patients good health care and new opportunities to find a place within the community. Clinicians and lawyers have to cooperate to define a fine balance between the patients’ rights and their needs for care.