Although radiography, computed tomography (CT), and magnetic resonance imaging are still the methods of choice for the study of lung cancer, they have certain limitations in the evaluation of mediastinal lymph node metastases. Positron emission tomography (PET) with 18F-fluoro-2-deoxy-D-glucose (FDG) has recently emerged as a practical and useful imaging modality in patients with lung cancer. We evaluated the usefulness of FDG-PET in the detection of mediastinal lymph node metastases and then compared the findings with the results of CT by region based on the histological diagnosis. For FDG-PET, the sensitivity, specificity and accuracy were 93%, 76%, and 98%, respectively, whereas, for CT, this was 65%, 87%, and 82%, which showed significant differences. FDG-PET is significantly more accurate than CT in lymph node staging of lung cancer, and also can improve the diagnostic accuracy in distant metastases.