Lymph node enlargement of five centimeters in the lungs may be caused by lung diseases, but also other systemic diseases such as immune system diseases, we should consult the doctor in time to clarify the cause of the disease, and symptomatic treatment for the cause. 1. Pneumonia: Pneumonia is usually caused by bacterial infection, if the treatment is not timely, the surrounding lymph nodes will be enlarged, which may cause lymphadenitis. 2. Lung cancer: the most common metastatic site of lung cancer is lymph nodes. Therefore, metastasis of lung cancer will cause lymph node enlargement. Generally, metastasis of lung cancer to the opposite hilar and mediastinal lymph nodes needs to be treated with surgery and radiotherapy. 3. Tuberculosis: Tuberculosis is mainly a specific inflammation of lungs caused by tubercle bacillus. Inflammation reaches the hilum along the lymphatic system, causing lymphatic enlargement, so one of the main clinical symptoms of primary tuberculosis is the enlargement of hilar lymph nodes. 4. Autoimmune diseases: autoimmune diseases can also make lymph nodes enlarged, such as tuberculosis, which can also make lymph nodes enlarged. 5. Metastasis of other tumors: metastasis of some tumors can cause enlarged lymph nodes, mainly because the blood supply of lungs is richer, while other tumors can reach lungs through pulmonary circulation, thus causing enlarged lymph nodes. 6. Blood system diseases: Blood system diseases may cause enlarged hilar lymph nodes, such as lymphoma, which can also cause enlarged hilar lymph nodes. It is recommended to go to the hospital for examination, and the doctor will make a judgment according to the clinical symptoms, and clarify the cause of the disease and treat the symptoms in time.