CT examinations in 37 patients with proved small-cell bronchogenic carcinoma studied before treatment were reviewed. The distribution of lymphadenopathy in the mediastinal compartments designated by the American Thoracic Society was assessed. The frequency of lymph node enlargement was right hilum (43%), left hilum (49%), one or both hila (84%), right upper paratracheal (32%), right lower paratracheal (54%), right tracheobronchial (65%), left upper paratracheal (14%), left lower paratracheal (38%), left peribronchial (35%), paraesophageal (14%), anterior mediastinum (24%), and subcarinal (65%). We also assessed the frequency of additional findings including pleural effusion (38%), pericardial thickening (38%), displacement or narrowing of either the tracheobronchial tree (68%) or major vessels (68%), and hepatic masses (24%). Mediastinal involvement was present in 92% of cases, as compared with 13% reported in a large series based on conventional radiography. These data show the spectrum of intrathoracic CT findings in proved, untreated cases of small-cell bronchogenic carcinoma.