To evaluate the sensitivity and specificity of transthoracic fine needle aspiration cytology(TFNAC) in the preoperative diagnosis of pulmonary nodules, a retrospective analysis was carried out on a consecutive series of 200 TFNACs. They included 186 primary malignant tumors, 66 squamous cell carcinomas, 65 adenocarcinomas, 36 small cell carcinomas, 7 large ceil carcinomas, 4 carcinomas, 8 others, 9 metastatic tumors, and 5 benign tumors. On cytohistologic correlation of malignant pulmonary tumors, the procedure had a sensitivity of 97.3% and a specificity of 100%. A 86.6% correct correlation between the cytologic and histologic diagnoses was achieved. Five out of the 7 undifferentiated large cell carcinomas, 10 out of the 65 adenocarcinomas, 2 out of the 36 small cell carcinomas, and 2 out of the 66 squamous cell carcinomas were turned out to be mistyped in cytologic diagnosis. We concluded that TFNAC is a highly sensitive and specific preoperative diagnostic procedure in the investigation of patients with discrete pulmonary nodules in whom the specific ceil type of the malignant neoplasm has important implications in treatment modality and prognosis.