A ground glass nodule of 0.5 cm or 5 mm in the lung is less likely to be a lung cancer. According to the recommendation of the guideline, a ground glass nodule of 8 mm or larger is required for further dynamic observation to exclude the possibility of lung cancer, so for such a small nodule, dynamic follow-up observation is sufficient. If a 5mm pulmonary ground glass nodule is found on physical examination, it can be reexamined once after 3 months. If the disease is still stable, a CT scan of the lung can be done once in 0.5-1 year without much concern, as a 5mm nodule may be lung cancer in a few cases, but the chance is very low.