A total of 130 patients with clinically suspected primary or secondary malignant neoplasms of the lung underwent fine needle aspiration biopsy under fluoroscopic control. The cases included 80 primary malignant tumors of the lung, 35 metastatic deposits, 14 nonneoplastic lesions and 1 benign tumor. The cytologic diagnoses were confirmed histologically in 56 cases and clinically in 74. Among the latter, the cytologic findings were comparable to the histology of the primary tumor in 19 cases with metastatic pulmonary lesions; in five cases, the extrapulmonary primary was identified on the basis of the cytologic study of the metastatic pulmonary lesion. The diagnostic sensitivity was 0.91 because of a false-negative result in a case of bronchial carcinoid, and the diagnostic specificity was 0.95. The predictive value was 0.99 for positive results because of a false-positive diagnosis given on a chondroid hamartoma and 0.70 for negative results. The sensitivity was 0.92 for primary malignancies and 0.89 for metastases. The cytologic typing accuracy of the 32 cases with histologically confirmed primary carcinoma of the lung was 0.65. Large-cell carcinoma and adenocarcinoma were the types that were cytologically unidentifiable most frequently. No major complications caused by the procedure were recorded in the present series.