INTRODUCTION: Transthoracic fine needle aspiration biopsy(TNAB) has shown to be a resonably safe, simple, and accurate procedure in diagnosis of intrathoracic lung lesions. We reviewed the results of 1,005 TNAB of chest lesions performed on 930 patients with 20 or 22-gauze needles over a period of 10 years. METHODS: From November 1983 to June 1995, 1,005 cases in 930 patients with an undiagnosed lung lesion underwent TNAB at the Hanyang University Hospital: 66% were men and 34% were women. Most of the patients were 40~60 years old and the youngest patient was 3 years of age. RESULT: 540 patients had various malignant chest lesions and 322 patients had benign pulmonary lesions. The diagnostic accuracy of TNAB was 96.1 percent in malignant diseases with one false positive result and 90.1% in benign diseases. A definitive diagnosis was not obtained in the remaining 68 patients. The most common diagnoses among 519 malignancy chest lesions with TNAB were the following: squamous cell lung carcinoma, 31.7%; adenocarcinoma, 24.7%; small cell lung carcinoma, 16.7%; metastatic cancer, 14.2%; large cell lung carcinoma, 6.2% and so on. Complications included pneumothorax in 12.3% necessitating chest tube drainage in 0.6%. Minor hemoptysis occurred in 3.6%. There was no death directly attributable to the procedure. CONCLUSION: We concluded that TNAB permits a direct approach to all kinds of localized lung lesions with a high degree of accuracy and without major complications.