Ninety-two fine-needle aspiration biopsies (FNAB) were performed in 79 patients, yielding a sensitivity of 90 percent and specificity of 100 percent for malignancy. Seven different malignant cell types were identified: squamous cell, adenocarcinoma, large cell, small cell, carcinoid, embryonal cell, and malignant fibrous histiocytoma. A 94 percent correct correlation between the cytologic and histologic specimens was achieved. Pneumothorax requiring tube thoracostomy complicated 11 percent of the biopsies. Thoracotomy was avoided in 35 percent of patients considered for operation because FNAB documented benign disease, metastatic disease, or small-cell carcinoma. FNAB was able to provide a pathologic diagnosis for chemotherapy and radiotherapy in patients with metastatic disease. A diagnosis was obtained prior to operation in 98 percent of thoracotomies. Only one diagnostic thoracotomy and one thoracotomy for unresectable pulmonary malignancy were required in a 4-year period. We concluded that FNAB, a highly sensitive and specific procedure with a low morbidity rate and a high correlation with histologic findings, reduces the need for diagnostic thoracotomy.