The causes of swollen lymph nodes are numerous and can be divided into two categories: infectious diseases and non-infectious diseases. Infectious diseases can be classified in more detail according to the pathogen. Viral infections such as EBV, cytomegalovirus, HIV, bacterial infections such as Streptococcus pyogenes, fungal infections, tuberculosis, and parasitic infections can all cause swollen lymph nodes. In non-infectious diseases, including autoimmune diseases and neoplastic diseases, we should pay attention to lymph node enlargement due to lymph node metastasis caused by tumors of solid organs, as well as to hematologic diseases such as lymphoma.