Between January 1986 and January 1991, 175 patients with suspected T3 or T4 bronchogenic carcinoma underwent computed tomographic (CT) examination of the chest before thoracotomy. We considered two groups of patients: group 1 includes 98 patients with a paramediastinal mass on standard chest X-ray; invasion of hilar and mediastinal structures was preoperatively investigated with CT and then assessed at thoracotomy. The sensitivity, specificity and accuracy were 72%, 75% and 73%, respectively; positive and negative predictive values were 71% and 76%. In group 2 77 patients had a peripheral tumor suspected of invading the parietal pleura and the soft tissues of the chest wall (patients with evident rib or vertebral invasion were not included). Sensitivity, specificity and accuracy of CT were 52%, 86% and 71%, respectively; positive and negative predictive values were 74% and 70%. We conclude that CT with injection of contrast material is indispensable when direct lung cancer infiltration must be ruled out; its accuracy is however not sufficient to be relied upon in all patients.