We evaluated the accuracy of computed tomography (CT) and of surgical assessment for lymph node staging prospectively in 108 patients with bronchogenic carcinoma. For CT/surgical assessment a sensitivity of 29/90%, a specificity of 93/63%, a positive predictive value of 49/39% and a negative predictive value of 85/96% were calculated on a node-by-node basis. Sensitivity and specificity of CT were highly influenced by the lymph node region studied and by typing of the tumor. Adenocarcinomas showed a high proportion of normal-sized metastatic lymph nodes whereas squamous cell carcinomas exhibited a high proportion of enlarged tumor-free lymph nodes. The diagnostic accuracy in predicting the correct N-stage by CT was determined with 54% for squamous cell carcinoma and 56% for adenocarcinoma. The surgeon predicted the N-stage correctly in 39% of squamous cell carcinoma and 69% of adenocarcinoma. In conclusion, accuracy of CT-scan is too low to renounce mediastinoscopy for routine use in preoperative staging of bronchogenic carcinoma.