BACKGROUND: Transthoracic fine needle aspiration and biopsy(TNAB) has become a frequently used technique in the investigation of the intrathoracic lesions because of its safety, reliability, and accuracy. METHOD: Data on 125 patients who underwent TNAB from 1990 through 1994 were studied to determine the diagnostic sensitivity, accuracy and complications of this procedure as related to lesion type and location. RESULTS: 1. The over-all diagnostic sensitivity of TNAB was 61.6%(77 of 125 patients). 2. The diagnostic yields were as high as 89.9% for malignant lesions, but a specific diagnosis of benign lesions were obtained only in 30% of benign lung lesions. 3. The correlation between results of TNAB cytology and of final histology was as high as 88.2%. 4. Lung lesions that were greater than 3cm in size had a higher proportion of correct diagnosis(73.3%) as compared with lesions 3cm or less in size(38.1%). But there was no significant difference between the central and peripheral lung lesions. 5. There were no serious complications to TNAB. In 12.8% of the procedures a pneumothorax developed, indicating a chest tube in 1.6% of the procedures. In 2 cases, minimal hemoptysis developed which did not require treatment. CONCLUSION: In our experience, TNAB represents a minor and safe procedure, which permits a direct approach to localized malignant lung lesions with a high degree of accuracy.