Tuberculin test was first used as a diagnostic test of tuberculous infection during the first decades of this century. From the up to date, no other method has proven to be more efficient for this task. In the present work we try to explain what the test consists of, what is its use, how it is interpreted, and which are the indications for the Mantoux intradermal reaction. We emphasize the importance of performing this technique correctly so as to not invalidate the results of this test which is essential both from a individual as from an epidemiological point of view.