Submandibular lymphadenitis is divided into acute and chronic lymphadenitis, depending on the cause. Acute submandibular lymphadenitis is usually caused by Staphylococcus aureus or Streptococcus hemolyticus infection, mostly secondary to other septic infections such as pharyngitis, tonsillitis, rhinitis, and mouth ulcers. Chronic lymphadenitis is usually divided into two types, non-specific lymphadenitis and tuberculous lymphadenitis. The former can be caused by the extension of acute lymphadenitis, but most of the causes are unknown. In patients with this type of lymphadenitis, there is no difficulty in diagnosis if there is a clear past history of acute lymphadenitis. However, in patients with unknown causes, it is important to know in detail the organs surrounding the patient’s enlarged lymph nodes to avoid missing the enlarged lymph nodes caused by tumor metastasis in certain areas.