The CT, surgical and histological findings were examined of 350 lymph nodes in a perspective study of 50 patients affected with lung cancer. CT accuracy could thus be evaluated in assessing the size of hilar and mediastinal lymph nodes; the incidence of histologically-proven metastases in nodes more/less than 10 cm in diameter could also be determined, together with CT diagnostic accuracy for nodal metastases. Finally, CT capabilities were also evaluated in distinguishing N0 from N1-N2 patients. CT proved to have high negative predictive value and low positive predictive value, which caused the authors to raise the normal threshold value of CT evaluation of the greatest diameter for hilo-mediastinal nodes from 10 to 20 mm.