The historiographical prejudice that sees in Jean-Jacques Rousseau an implacable opponent of scientific knowledge has long prevented an objective evaluation of the important influence that medical thought exerted over his philosophy. The aim of this paper is to show not only Rousseau's familiarity with the most important expressions of eighteenth-century medical literature, but also his willingness to incorporate some medical suggestions in his philosophical and literary production. In the first part of this article, I try to show how Rousseau's sensibility theory presupposes precise medical ideals, related to Montpellier School of vitalism. In the second part, I stress how Rousseau's philosophy of alimentation (which has clear anthropological and political implications) can be regarded as a genuine application of an ambition typical of vitalism: to use medical hygiene, also and above all, for moral purpose.