Background : The observation made by the ASTER investigators might be criticized as all procedures were performed in highly experienced centers. To date, the number of mediastinoscopies needed to detect one additional N2/3 disease in the routine clinical practice of chest physician performing endosonography for mediastinal staging is unknown. The investigators therefore seek to answer whether a negative endosonography should routinely be followed by mediastinoscopy in day to day clinical practice.