Whether a small nodule in the lung is important or not needs to be determined by the nature of the nodule. Small nodules in the lungs are relatively common, mostly due to inflammation in the lungs, but malignancy cannot be ruled out, so they should be reviewed and attended to regularly. Small nodules in the lungs are usually related to the working environment and living habits, and are more common in people who have a lot of mites and dust in their work and who smoke for a long time. In addition, tuberculosis, autoimmune disease, vasculitis, infection, and pulmonary nodular disease can all cause small nodules in the lungs. In general, there is a correlation between nodule size and the chance of malignancy, and the larger the nodule, the higher the risk. If the nodule continues to increase in size, it is important and further testing is needed for the possibility of malignancy. When a small lung nodule appears, the patient can be reviewed after 3 months. If the nodule is not significantly enlarged at the time of review, it is more likely to be benign and still needs to be followed up for 3-5 years thereafter. If there is significant enlargement, further intensive CT of the chest and examination of lung tumor markers are recommended.