The value of computed tomography (CT) for the diagnosis of non-small-cell primary bronchogenic carcinoma with regard to T and N classifications was prospectively evaluated in a series of 29 patients. The sensitivity of CT in evaluating the extension of tumor to pleura or mediastinum was 100%, with only a 76% specificity. Computed tomography demonstrated 73 lymph nodes greater than or equal to 10 mm and 55 lymph nodes less than 10 mm in 27 patients. Invasive staging showed 23 lymph nodes greater than or equal to 10 mm and 22 nodes less than 10 mm which were not visualized by CT. Malignant invasion was found at histology in only one of these lymph nodes. The majority of nodes not visualized by CT were localized in the left paratracheal group, right and left tracheobronchial groups and the aortopulmonary window.