An analysis of 1,454 percutaneous thin needle biopsies (PTNB) performed in 1,061 patients in the years 1976-1987 disclosed the sensitivity for the detection of malignancy 93.7%, specificity 95.8%, and accuracy 93.9%. The most commonly encountered indication for PTNB was a solitary lung lesion (56% of 1,061 patients), with a rate of true positive cytologic findings 93.4% of patients with proved malignant tumours. Indications for PTNB included pulmonary opacities of or without recognizable segmental distribution, enlargement of mediastinum or hilus, lesions of the pleura or chest wall, and cavitary lesions, with results not significantly worse than in circumscribed peripheral lesions. Pneumothorax occurred in 18%, hemoptysis in 1.9%, other minor complications very rarely. PTNB appears to be a safe, reliable, and accurate technique for diagnosing chest lesions with various types of roentgenographic image.