PURPOSE: To evaluate accuracy of magnetic resonance(MR) imaging for staging of lung cancer and to compare the accuracies of CT and MRI. MATERIALS AND METHODS: We retrospectively analyzed 25 cases of lung cancer, which were confirmed surgically and pathologically. Five experienced radiologists participated in the receiver operating characteristic (ROC) analysis to evaluate and compare accuracies of the CT and MR imaging in preoperative staging of non small cell lung cancer by assessing tumor invasion of bronchus, mediastinum, chest wall, and hilar or mediastinal lymph node metastasis. Imaging results were evaluated against "truth" data based on both surgery and pathologic examination. RESULTS: Sensitivity of CT in distinguishing T3-T4 tumors was 60% ;specificity was 76%. These values for MR imaging were not significantly different(53% and 72%). With ROC analysis, no difference existed between accuracies of CT and MR imaging in diagnosis of bronchial involvement, but MR imaging was significantly more accurate than CT(p<0.05) in diagnosis of mediastinal invasion. There was no significant difference between accuracies of CT and MR imaging in detecting mediastinal node metastasis(N2 or N3); sensitivities were 64% and 78%, respectively, and specificities were 64% and 66%. CONCLUSION: There was no significant difference in accuracies of CT and MR imaging in preoperative tumor classification and assessment of mediastinal node metastasis, but MR imaging was more accurate than CT in assessment of mediastinal invasion.