PURPOSE: To determine the ultrasonographic findings and assess the usefulness of ultrasound (US)-guided biopsy of central lung tumors in patients with obstructive pneumonitis. MATERIALS AND METHODS: Fourteen patients with central lung tumors causing obstructive pneumonitis, as seen on chest radiographs and chest CT scans, were examined between January 1997 and January 2000. In no patient conclusive histologic diagnosis obtained by means of bronchoscopic biopsy or sputum cytology. Eleven patients were men and three were women, and their ages ranged from 45 to 83 (mean, 64) years. For all examinations, real-time, linear-array, convex US units with a 3.75- and a 5.0-MHz transducer were used. The images obtained were analyzed for evidence of consolidation or atelectasis in the lung, demonstrable tumors, and tumor size and echogenicity. For US-guided percutaneous transthoracic biopsy, 19.5G automatic biopsy devices, were employed. RESULTS: Lung consolidation due to a wedge-shaped, homogeneous, hypoechoic lesion was revealed by sonographic fluid bronchograms, air bronchograms, air alveolograms, and visualization of intraparenchymal pulmonary vessels, which showed appropriate motion with respiration. The tumor presumed to be causing obstruction was seen as a hypoechoic nodule near the hilum or as a well-defined hyperechoic mass inside the partially consolidated lung. Pleural effusion was observed in one case. The cytologic findings indicated the presence of squamous cell carcinoma (n=4), adenocarcinoma (n=4), small cell carcinoma (n=3), non-small cell carcinoma (n=2) and large cell carcinoma (n=1). The success rate was 100%, and there were no complications. CONCLUSION: In patients with central lung tumors causing obstructive pneumonitis, chest ultrasonography and US-guided biopsy are useful adjunctive diagnostic modalities and techniques.