Small nodules on the lungs refer to round, round-like, dense shadows seen on a chest X-ray or CT of the lungs. Generally, those smaller than 3 cm are called nodules and those larger than 3 cm are called masses. The most common cause of a small nodule on the lung is a lung infection, or it may be an old lesion, or tuberculosis, nodular disease, or a malignant tumor of the lung. If the nodule is first considered to be a lung infection, antibiotics may be given for two weeks and then the lung CT may be repeated, and if there is no change, the lung CT may be repeated in, say, three months, and if there is still no change, the lung CT may be repeated in six months, and if there is still no change, the follow-up period should be decided under the guidance of the doctor. If adults older than 40 years old have a history of smoking or secondhand smoke, or have a family history of malignant tumors in their family, they should be reviewed regularly. If, in the course of follow-up, nodules are found to have changed in density or become larger, or some signs of malignancy, such as vascular signs, vacuolation signs, etc., further examination is required to further clarify the diagnosis.