There are many reasons why the lymph nodes in the neck may become enlarged, but the two most common causes are due to infection and cancers.
Another common cause of lymph node enlargement is from cancer. The cancer may arise primarily from the lymph nodes (e.g. lymphoma), but often they have spread to the lymph nodes from somewhere else (e.g. tongue cancer, nasopharyngeal cancer).
Some other less common conditions in which lymph nodes of the neck can be enlarged include: