By pulmonary nodules, we mean small, focal, round-like, image-opaque lesions less than or equal to 3 cm in diameter that are completely surrounded by air-containing lung tissue. There are no associated signs of pulmonary atelectasis, hilar enlargement, or pleural effusion, and they are usually asymptomatic. With the development of imaging techniques, especially the popularity of multilayer spiral CT, the detection rate of pulmonary nodules, small nodules, and even micronodules has increased significantly. Clinically, small lung nodules smaller than 5 mm have less than 1% probability of malignancy, and those 5-8 mm only need to be monitored closely and regularly according to medical advice. However, once they exceed 1 cm, the probability of malignancy increases significantly and need to be treated aggressively according to the imaging features. The nature of the nodules should be further defined by puncture biopsy, surgery for malignant ones, and regular observation for benign ones. There is usually a pattern of whether a small nodule is benign or malignant. Clinically, if a small nodule has smooth edges and internal calcified spots, it is usually benign, mostly due to tuberculosis or inflammation, and can be actively treated symptomatically. On the other hand, malignant nodules are mostly irregular in shape, with unsmooth edges, burr-like and lobulated, which are mostly manifestations of early stage lung cancer. When small nodules are detected at an early stage, follow-up can be chosen, and the interval of follow-up depends on the size and density of nodules. For small lung nodules less than 0.8 cm in diameter, low-dose spiral CT is usually performed at the 3rd, 6th and 12th months for 2-3 years of continuous observation. If there is no change in size then the examination is extended as prescribed by the doctor, but periodic examinations are still required. If the nodule is found to be enlarged, or if the patient develops symptoms, a pathological diagnosis needs to be obtained as soon as possible, and puncture biopsy is a more widely used diagnostic method to further clarify the nature of the small nodule, whether it is malignant or benign, and to decide whether it needs to be surgically removed. Even for lung cancer, if detected early and treated by minimally invasive surgery, the 5-year survival period can be over 80%. Therefore, people must pay attention to the discovery of lung nodules, early detection, early diagnosis, and timely treatment if the nature is clear, which can effectively improve the cure rate of lung cancer. For high-risk groups such as those who are older than 60 years old, long-term heavy smokers (those who smoke more than 1 pack per day) and those with family history of tumor, it is necessary to routinely have a low-dose spiral CT examination of the chest once a year.