Transthoracic needle aspiration biopsy (TNAB) of lung lesions is a well established procedure for diagnosing lung lesions. The emphasis in the literature has been on diagnosing malignant lesions with an accuracy rate greater than 90% frequently reported. Experience with 650 patients showed that TNAB can diagnose malignant lesions in 95% of patients with cancer, and more importantly that TNAB can identify benign lesions in 88% of patients with such lesions. In this patient population, 22% of undiagnosed, noncalcified lung lesions were benign. Therefore, TNAB of lung lesions has a potential of limiting diagnostic thoracotomies to fewer than 8% of patients with lung lesions, significantly reducing the number of unnecessary thoracotomies for benign disease. The success of TNAB is affected by equipment, technique, skill, and experience and is enhanced by close cooperation among the various physicians involved.