Aim: In this study, the role of thorax-CT was examined in evaluating intrathoracic lymph node in patients diagnosed with preoperative Non-Small Cell Lung Cancer (NSCLC). This study aims to review our existing knowledge on thorax-CT, which is the first examination method used in the evaluation of lung masses and to discuss its performance in mediastinal staging based on data of patients in Turkey. Material and Method: 510 cases selected by the criteria identified between January 2009 and July 2011 were included in the study. Lymph nodes, their sizes in thorax-CT, histological type of the tumor, removed mediastinal lymph nodes and pathology results were examined. Results: As a result of the statistical analyses, the sensitivity of thorax-CT in detecting metastatic intrathoracic lymph nodes was calculated as 75.7%, specificity 41%, negative predictive value (NPV) 85% and accuracy 48.4%. NPV and positive predictive value (PPV) were also calculated for N1 and N2 diseases. False positive rate of thorax-CT in detecting N1 disease was calculated as 53.6%, and the false negative rate was calculated as 28.7%. The false positive rate in detecting N2 disease was 64.6%, and the false negative rate was 20%. Discussion: While thorax-CT is essential in mediastinal staging in NSCLC, we believe that thorax-CT alone is not sufficient and needs to be supplemented with other scans and invasive methods. Due to the increased health costs, the waste of time and labor due to the use of more than one scan, Positron Emission Tomography and CT should be used more frequently in especially in lung cancer.