As the technique of percutaneous lung biopsy continues to evolve, it offers an increasingly accurate method of establishing the malignancy or benignity of a solitary pulmonary nodule. There are relatively few contraindications to the procedure, and the complications-primarily pneumothorax and hemoptysis-generally resolve without therapy. Transthoracic needle aspiration has an important role in the workup for a "coin lesion." Other elements of the diagnostic workup-particularly the history, a chest roentgenogram, computed tomography, sputum cytology, and transbronchial brush biopsy-may either add to or substitute for a transthoracic needle aspiration biopsy. An algorithm can be used to guide the diagnostic approach to a solitary pulmonary nodule.