This book analyzes the medical diagnosis outside the empiricist budgets instituted in current medicine, based on elements from Philosophy, Humanities and Social Sciences. Here, the author invites us to consider medical practice from the Language Sciences, especially from Peircian Semiotics. In its cognitive dimension, the diagnosis is presented as an inferential process organized according to an abductive logic. In the diagnosis’ practice, doctors apply a great semiotic activity, an interpretation, a reading of the patient’s body, which cannot be reduced to the simple collection of evidence or to the mere empirical verification.