Abstract: Objective : To evaluate the correlation of lymph node size and their infiltration by metastases in lung cancer. Methods : In a morphometric study, hilar and mediastinal lymph nodes from 258 patients with non-small cell lung cancer (NSCLC) were analyzed. The lymph nodes were counted, the largest diameter of each lymph node was measured, and each lymph node was analyzed for metastatic involvement by histopathologic examination. The frequency of metastatic involvement was calculated and correlated with lymph node size. Preoperative CT scans of 80 patients were retrospectively analyzed. Lymph node size was measured, and lymph nodes were evaluated due to radiologic criteria. The radiologic evaluation was compared to the histopathologic diagnosis. Results : A total of 2 892 lymph node were present in the 258 specimens examined for this study. One hundred forty patients had a pNO status, whereas 118 patients had lymph nodes that were positive for cancer. Two thousand four handred eighty-seven lymph nodes (86%) were tumor-free, while 405 (14%) showed metastatic involvement on histopathologic examination. The mean diameter of the nonmetastatic lymph nodes was 7.05 ±3.7mm, whereas infiltrated nodes had a diameter of 10.7±4.7mm (P<0.005). One thousand nine hundred fifty-four of the tumor-free lymph nodes (78.5%) and 180 of the metastatic lymph nodes (44.3%) were<10mm in diameter. Of 140 patients with no metastatic lymph node involvement, 102 (73%) had at least one lymph node that was >10 m m iniameter. Of 118 patients with metastatic lymph node involvement, 13% had no lymph node that was >10 mm. The independent radiologic evaluation of the CT scans of 80 patients yielded a sensitivity of 57% and a specificity of 80.2%. Conclusion : Lymph node size is not a reliable parameter for the evaluation of metastatic involvment in patients with NSCLC.