Abstract: Objective To evaluate the value of mediastinoscopy in cases of positive mediastinal/hilar lymph node involvement in positron emission tomography and computed tomography（PET/CT）scanning in nonsmall cell lung cancer. Methods NSCLC cases with mediastinal or hilar involvement in PET/CT treated by mediastinoscopy were retrospectively analyzed. The sensitivity, specifi city, positive predictive value (PPV), negative predictive value (NPV) and accuracy rate of PET/CT and the false positivity of mediastinoscopy in mediastinal staging were calculated. Results Between Apr 2007 and Dec 2011, 73 NSCLC cases were enrolled. The sensitivity, specifi city, PPV, NPV and accuracy rate of mediastinoscopy in mediastinal staging were 91.3%,100%,100%,87.1% and 94.5%,respectively . The the false positivity of PET/CT was 30.8%. If non-bulky mediatinal lymph nodes with bilateral hilar distribution were considered benign, PPV of PET/CT was increased to 81.1%. Conclusion Mediastinoscopy has high sensitivity, specifi city in mediastinal staging in NSCLC cases with mediastinal or hilar involvement in PET/CT. Positive mediastinal involvement in PET/CT, especially bilateral hilar distribution needs to stage by invasive methods.