Two hunderd and seventy patients with thoracic lesions (including 10 patients with chest wall lesions, 36 with pleural lesions, 130 with intrapulmonary lesions, 81 with mediastinal lesions and 13 cases with partial or complete opacity of hemithorax) were evaluated by ultrasonography during a period of 58 months from January 1987 to October 1991. The value and limitation of ultrasonography in the diagnosis of thoracic lesions were discussed on the basis of comparison with radiographic diagnosis. In 125 of 270 patients percutaneous needle biopsies guided by ultrasonography were performed with an accuracy rate of 97.5%. Slight amount of pneumothorax occured in only two cases (1.60%) after the biopsy.