Pulmonary nodules are round lesions less than 3 cm in diameter that appear in the lungs; among them, lesions greater than or equal to 1 cm in diameter are called large nodules; those less than 1 cm are called small nodules. With the advent of imaging techniques such as high-resolution CT of the chest, more and more small nodules are being detected before the clinic, how to determine whether they are benign lesions or fearful malignant tumors? Physicians can improve the diagnosis of small pulmonary nodules by combining high-resolution CT (HRCT), especially spiral CT, to magnify the local morphology of the lesion and observe its surroundings. The nature of the lesion is often determined clinically by a combination of the imaging characteristics of the small nodule and its dynamic changes, as well as the patient’s own symptoms. The international Fleischner Society guidelines for the management of small pulmonary nodules, which incorporate multiple lines of evidence and are currently widely used, classify the observed population into low-risk and high-risk patients, with high-risk patients including smoking and known risk factors (including chronic lung disease, history of lung tumors, etc.). I. For the low-risk group Nodules less than or equal to 4 mm: no follow-up; 4-6 mm: 12-month follow-up, stop if no change; 6-8 mm: 6-12-month follow-up, 18-24-month follow-up if no change; greater than 8 mm: 3, 9, 24-month enhanced CT, PET or puncture. Second, for high-risk groups: nodules less than or equal to 4mm: follow up once in 12 months, if no change, stop; 4-6mm: follow up once in 6-12 months, if no change, follow up once in 18-24 months; 6-8mm: follow up once in 3-6 months, if no change, follow up once in 18-24 months; more than 8mm: same as low-risk groups. It should also be noted that: 1. Patients with known malignancies should be followed up for a shorter period of time; 2. The incidence of lung cancer in people under 35 years of age is extremely low, less than 1%, and they are sensitive to radiation, so follow-up needs to be cautious and should be low-dose scans; 3. Patients with fever should consider the possibility of inflammation, and review after anti-infection or short-term review is recommended; 4. Lung cancer is more common in lesions located in the upper lobe; 5. Screening detects a significantly higher lethality of cancer in patients who smoke than 6. Nodules smaller than 4 mm are basically benign, and even for patients who smoke, the malignancy rate is less than 1%; 7. Screening lesions larger than 8 mm have a 10-20% chance of malignancy and should be treated more aggressively.