Bilateral axillary lymph nodes 12×5 mm may be caused by axillary lymphadenitis, connective tissue disease, tumor, etc. Whether it is serious or not is related to the causes of lymph node enlargement. 1. Axillary lymphadenitis: bilateral axillary lymph node enlargement may be caused by axillary lymphadenitis, which is mainly related to bacterial and viral infections. Generally speaking, after active anti-viral and anti-infection treatments, patients’ lymph node enlargement will be gradually relieved or disappeared, which is generally not serious. 2. Connective tissue disease: some patients with swollen lymph nodes in the armpit may be caused by connective tissue disease, such as systemic lupus erythematosus, tuberculosis, etc., the patient can be actively treated, generally not serious. 3. Malignant tumors: Some patients may have lymphatic metastasis of malignant tumors, lymphoblastic leukemia, or lymphoma and other diseases, which are often more serious and require early and active treatment. When bilateral axillary lymph nodes are enlarged, patients need to clarify the cause of the disease at an early stage.