To determine more precisely the role of mediastinoscopy in the preoperative staging of bronchogenic carcinoma, we studied 85 patients in the period 1983 to 1985 and compared the results of mediastinoscopy and computed tomographic scanning with the findings at thoracotomy. Mediastinoscopy was performed in 48 patients when mediastinal nodes larger than 1 cm were found at computed tomographic scanning. Only 21 of them (44%) were found to have metastatic nodes. Of the remaining patients, 22 were operated on and two showed false negative results (9%). Mediastinoscopy had a sensitivity of 91% and a specificity of 100%. The positive predictive value of computed tomographic scanning was only 54%. Thirty-seven patients underwent thoracotomy after having negative computed tomographic scan results. Eleven of them (30%) were found to have metastatic mediastinal lymph nodes. The negative predictive value of computed tomographic scanning was 70%. When results from both series of patients were compared, the sensitivity and specificity of computed tomographic scanning proved to be 68% and 57%, respectively, with an accuracy of 61%. Because of the low accuracy rate of computed tomographic scanning, a more routine use of mediastinoscopy seems to be justified.