Milled glass nodules in the dorsal segment of the lower lobe of the left lung are the presence of lung nodules containing a milled glass component in the dorsal segment of the lower lobe of the left lung, which may be a benign or malignant disease of the lung. Normal people have left and right lungs, and the left lung is divided into upper and lower lobes. The lower lobe of the left lung includes the upper (i.e., dorsal), inner anterior basal, outer basal, and posterior basal segments. Lung nodules can be categorized into three types according to their composition: solid nodules, pure ground-glass nodules, and mixed ground-glass nodules, which are collectively known as ground-glass nodules. The malignancy rate of pure ground glass nodules is slightly lower, at about 18%, whereas the malignancy risk of mixed ground glass nodules is higher, at about 63%. Therefore, ground glass nodules in the dorsal segment of the lower lobe of the left lung have a certain risk of malignancy, and may be either malignant tumors such as lung cancer or benign diseases such as pneumonia, tuberculosis, and charcoal deposition, etc. It is necessary to make a comprehensive judgment of the possible etiology based on the descriptions of the nodule’s size and morphology, and the examination of the tumor markers and other tests. Patients are advised to consult a specialist for further examination and treatment as prescribed by the doctor.