Solitary pulmonary nodules are usually identified on routine chest radiographs in asymptomatic patients. Most nodules have a benign cause, but bronchogenic carcinoma, metastases, and other malignant processes are important causes as well and must be excluded in differential diagnosis. Plain chest radiography, computed tomography, and fine-needle aspiration biopsy are useful diagnostic tools. When a malignant cause cannot be ruled out, the patient's age, smoking history, and nodule size must be considered. Observation by serial radiographs may be the appropriate course for patients who are at low risk for malignancy. For moderate- and high-risk patients, an immediate and more invasive workup is indicated.