The presence of mediastinal lymph node metastasis in lung cancer has a great influence in treatment selection and prohnosis and the diagnosis of lymphatic metastasis must be accurate. CT chest scans and mediastinoscopy are the diagnostic tools available to detect mediastinal lymph nose metastases and tostabilish pre operative staging. Lymph node size evaluated by CT scans is not an acceptable criterion in our patients. The aim of this study is to find out a representative pattern of size to indicate the possibility of neoplasic invasion in our population. 50 consecutive patients were operated on and underwent pulmonary resection to treat lung cancer. 74 por cento of the lymph nodes with transversesection of than 3 cm had no neoplasic invasion. CT scand and mediastinoscopy have similar sensitivity ( close to 65 por cento ) but mediastinoscopy has higher specificity ( cem por cento ). This means that we must have histologic confirmation of any suspected lymph node to achieve a correct staging