Small nodular foci in the lungs may be a sign of lung cancer, but other conditions can also cause them to appear and are not absolutely relevant. Small nodular foci in the lung mainly refer to round or round-like shadows less than 3 cm in diameter found in the imaging of the lung. There are many causes of small nodular foci in the lung, and lung cancer is only one of them. Early stage of lung cancer, especially early stage of lung adenocarcinoma, can manifest as nodules in the lung. In addition to cancer, infectious diseases such as tuberculosis infection, fungal infection, or factors such as dust, cigarette, or atmospheric pollution can cause the appearance of lung nodules. When small pulmonary nodule foci appear, it should be further evaluated whether it is a chronic inflammatory or tumorigenic change based on high-resolution CT of the chest and enhanced CT of the chest. Patients should not be too nervous, it is not necessarily lung cancer.