Painful swollen lymph nodes behind the ear can be caused by infection, tumor and infectious mononucleosis. 1. Infection: when there is inflammation in the auricle, external auditory canal, middle ear, parotid area, nasal cavity, sinus, throat and other parts of the body due to infection, the lymph nodes behind the ear may drain into the ear causing inflammation and enlargement of the lymph nodes behind the ear, accompanied by pain. 2. Tumor: when there are lymph node tumors behind the ear or lymph node metastasis of tumors in the auricle or parotid gland, due to the tumor growing too fast or too big, or secondary infection, it can also lead to swelling and pain of lymph nodes behind the ear. 3. Infectious mononucleosis: the early onset of this disease may cause lymph node swelling in the whole body, including the lymph nodes behind the ear, and lymph node pain may also occur when secondary infection occurs. When the swelling of lymph nodes behind the ear occurs, it is necessary to go to the hospital in time to find out the cause of the disease and carry out the treatment, so as to avoid the delay of the disease.