Stroke is an acute and severe pathology, which can lead to rapid death or severe neurological motor and / or cognitive disability. In the most severe situations, medical action leads to consider withholding or withdrawal of treatments, if the prognosis appears to be "catastrophic", meaning most often the risk of "unacceptable" disability.The medical action in these situations is particularly complex. It raises the question of the purpose of the medical act in relation to the future quality of life of the patient, which involves the delicate estimate of the value of life, prediction inherently uncertain. But if the prognosis holds a central place in this action, other factors also play a role, such as the context. This thesis offers an exploration of the concepts of prognosis and “proportionality care” and an ethical approach based on taking into account the complexity and Aristotelian deliberation.