The majority of pulmonary ground glass nodules are benign, with only a small percentage being malignant. Overall the incidence of lung cancer in pulmonary ground glass nodules is 18%. Usually, the malignancy of ground glass nodules is related to their size, and the probability of malignancy is very low for micro nodules <2mm in diameter; 0%-1% for ground glass nodules <5mm in diameter; 33%-64% for ground glass nodules 11-20mm in diameter; and 64%-83% for ground glass nodules >20mm in diameter, so the larger the diameter of ground glass nodules, the higher the probability of malignancy. The larger the diameter, the greater the probability of malignancy. Common clinical causes of ground glass nodules include lung cancer, inflammatory infections, such as tuberculosis infection, mycoplasma infection, fungal infection, etc. They can also be seen in allergic diseases, nodular diseases, connective tissue diseases, etc. If the nodule is malignant, it may have features such as lobar sign, burr sign, pleural involvement sign, vascular collection sign and vacuolation sign. Benign ground glass nodules tend to be dense nodules with smooth margins, usually with little vascular supply and no pleural involvement, or they can be low-density nodules, such as cysts, or calcified nodules. For small ground glass nodules regular follow-up is required, and CT examinations can be performed once every 6-12 months for ground glass nodules <5 mm in diameter. In the case of ground glass nodules >5 mm in diameter, the first follow-up is performed after 3 months, and thereafter a CT examination of the lungs should be performed once a year for at least 3 years of continuous monitoring.