The results of percutaneous thoracic aspiration needle biopsies in 221 patients performed over a 9-yr study period are presented. Indication for aspiration was a presumptive clinical diagnosis of primary or metastatic carcinoma of the lung or mediastinum. Of the 221 cases, 135 aspirates were reported as positive for malignancy, 26 were suspicious and 60 were diagnosed as negative or unsatisfactory. Follow-up data revealed 140 histologically and/or clinically confirmed cases of malignancy; of these 102 had aspirates diagnosed as positive, 15 as suspicious and 23 as negative. This represents a positive tissue diagnosis for malignancy of 73% from a minimally invasive technique within the study period. No false positive diagnoses were made.