Clinical decisions in daily practice, to resolve patient's problem, are usually based at the conscious use of the available information, through explicit determined rules. Evidence based clinical practice recognize the explicit and tacit knowledge, understanding that it is impossible all the aspects of professional competence become explicit. The doubt becomes part of the decision process, identifying initially the unconscious component involved and after the explicit knowledge used. When we make a structured clinical question with a possible answer, it is necessary to remember that the doubt can be related to basics and of definition aspects of the disease or related to the patient's manager, like diagnose, treatment and prognosis. Along our medical life, both types of question are present, with proportional change as the experience increase along the clinical practice. The process to find an appropriate answer to the doubt, came out at patient's care, depends on how the parts of this process will be structured. The recommended form is known by PICO abbreviation, that means: P: patient or population, I: intervention or indicator, C: comparison or control and O: outcome, or the answer expected found at the scientific information bases. This is the first basic need to a successful search, and the second need is to find the key words that better describe each of the four components of the questions. Without this caution, the search at compute databases results in absence of information or in a lot of information that it is not related to our interest.