Purpose : To determine the accuracy of CT in the evaluation of mediastinal nodal metastases of non-small celllung cancer. Materials and Methods : Between November 1994 and June 1997, 178 patients with non-small cell lungcancer underwent thoracotomy and full nodal sampling. The results of preoperative CT scanning and of pathologicexamination of regional lymph node metastases were compared. Each scan was prospectively interpreted by one chestradiologist. Mediastinal lymph nodes were localized according to the lymph node mapping scheme of the AmericanThoracic Society and were considered abnormal if they exceeded 10mm in short-axis diameter. All accessible nodeswere either removed or sampled during thoracotomy. Results : Of the 178 non-small cell lung cancers, 90 weresquamous cell carcinoma, 60 were adenocarcinoma, 13 were brochioloalveolar carcinoma, ten were large cellcarcinoma, and five were others (basaloid, 1; sarcomatoid, 1; spindle cell, 1; adenosquamous cell, 2). A total of615 mediastinal nodal stations were obtained. The sensitivity of CT for the diagnosis of mediastinal nodemetastasis on a station-by-station basis was 21%, with a specificity of 93% (squamous cell carcinoma: 21% and 91%;adenocarcinoma: 20% and 95%, respectively). Sensitivities were higher for groups 7 and 5. In 13 bronchioloalveolarcarcinomas, no lymph node metastasis was found on either CT or pathologic examination. The sensitivity of CT forthe diagnosis of mediastinal node metastasis on a per-patient basis was 43%, with a specificity of 83%. Conclusion: Because of the relative insensitivity of CT for the detection of mediastinal lymph node metastasis, nodalsampling with mediastinoscopy or thoracotomy is essential in the staging work-up of non-small cell lung cancerother than bronchioloalveolar carcinoma.