This is a review of the basic concepts of evidence, medicine, evidence-based medicine and its effects. Evidence-based medicine is a contribution for statistical design and management, that allows the gathering of scientific information, but does not completely excluse bias. Its methodology proceeds with order and caution, generating a highly probable mass of knowledge. The quality of the information obtained from diverse sources such as meta-analysis to expert opinions is classified in different levels according to the strenght of the evidence in which it is based. The best contribution of evidence-based medicine is probably for diseases of incidence and does not replace clinical experience and patients-physician relationship. Basically we treat ill people and not illnesses. Without clinical experience, medical practice can be tyrannized by evidence-based medicine that can become inapplicable or inappropriate. Without evidence-based medicine, medical practice will not be updated limiting our professional skills (Rev Med Chile 2005; 133: 1252-8).