The best approach to the initial management of solitary pulmonary nodules is controversial. Using decision analysis, we compared the average life expectancy produced by alternative strategies for managing the patient with a solitary pulmonary nodule: thoracotomy for diagnosis and potential resection (IMMEDIATE SURGERY); needle aspiration biopsy or bronchoscopy (BIOPSY) followed by either thoracotomy or extended observation, depending on the results of the biopsy; and serial chest films with thoracotomy if the nodule grows at a potentially malignant rate (OBSERVATION). IMMEDIATE SURGERY produced a slightly longer average life expectancy when the probability of cancer was very high; BIOPSY had a narrow advantage when the probability of cancer was intermediate; and OBSERVATION produced slightly longer average life-expectancy when the probability of malignancy was very low. But the differences between strategies were so small that, in most circumstances, the decision was a "close call." Therefore, when choosing between these management strategies, physicians should give greater weight to considerations besides life expectancy, and should encourage patients to actively participate in the decisions about how to manage their solitary pulmonary nodules.