Given the large number of publications, it is a problem to choose a study to respond to clinical problems with a good level of evidence. This requires following a scientific methodology, defining and limiting the problem, transforming it into a question, applying a search strategy in an appropriate source of information and finally, analyzing the information and summarizing the evidence found. Specific tools for analize the evidence had been develop. They are known as reading guides, Reader's Guides or Users' Guides, of which there are distinct formats, but in general, they give the necessary guidelines for the critical analysis of the different tipes of biomedical articles. These tools assess three key areas of study: internal validity, impact and external validity. The areas above mentioned are practically evaluated applying a user's guide to articles relating to treatment, as an example to a study published in a prestigious scientific journal.