The most common cause of microscopic lung nodules is a lung infection, but of course it can also be an old lesion, or tuberculosis, pulmonary nodular disease, or in rare patients, a malignant tumor of the lung. If a lung infection is considered, the anti-infection is reviewed after two weeks, and if there is no change, it is reviewed periodically. If there is still no change, go back for a lung CT after six months. if there is still no change, decide the interval of follow-up under the guidance of the doctor. For those who are over 40 years old, have smoked for a long time or have been exposed to second-hand smoke for a long time, and have family members with malignant tumors, regular follow-up must be emphasized. If, in the course of follow-up, nodules become larger or become unevenly dense, and signs of malignancy such as vacuolar signs, vascular signs, pleural depression signs, and lobarization appear, further examination must be performed for early diagnosis and early treatment.