For a century, the diagnosis of tuberculosis, based on bacilloscopy and the isolation and identification of Mycobacterium tuberculosis in cultures, has been slow and not very sensitive. This has made it necessary on occasions to initiate treatment with tuberculostatics in an empirical way. The routine incorporation of liquid mediums and molecular genetic techniques in the final decade of the XX century brought an important advance by clearly increasing the sensitivity, precision and rapidity of diagnosis. The present blossoming of molecular techniques is making possible a better understanding of the disease's epidemiology, the factors of virulence and the mechanisms of resistance, which in the near future will give rise to new strategies of prevention and for treating the disease.