Mediastinal lymph node metastasis (MLNM) is the most important prognostic factor and guide to the treatment in non-small cell lung cancer (NSCLC) patients with no distant metastasis. As a non invasive method, using of positron emission tomography (PET) to evaluate NSCLC is increasing. We aimed to compare results of PET and mediastinoscopy to reveal effectiveness of PET in the mediastinal staging of NSCLC patients. PET was performed to 100 operable NSCLC patients between 2004 and 2006. Later, standard cervical mediastinoscopy was performed to all of the patients. Twenty-six patients who detected MLNM at mediastinoscopy were referred to oncology clinic for neoadjuvant or definitive chemo-radiotherapy. Other 74 patients underwent thoracotomy and performed lung resection and mediastinal lymphatic dissection. Sensitivity and specificity rates for detecting mediastinal lymphatic metastasis of PET and mediastinoscopy were compared. There were 89 male and 11 female with mean age of 59 years. Sensitivity, specificity, positive predictive value, negative predictive value and accuracy rates were calculated as 74%, 76%, 59%, 86% and 76% respectively for PET and 83%, 100%, 100%, 93% and 95% respectively for mediastinoscopy. Accuracy rate of PET is not sufficient and mediastinoscopy is still the gold standard to evaluate mediastinal staging of NSCLC, at present.