A hard lump behind the ear may be clinically associated with the following conditions: the first is an enlarged lymph node behind the ear, which is more common with lymphadenitis, but also with lymph node tuberculosis or lymph node metastatic cancer. Ultrasound is recommended clinically to be able to identify them in general. The second type is lipoma behind the ear, which is mainly formed by abnormal fat metabolism behind the ear and is more likely to occur in obese patients. The third type is other diseases behind the ear, such as sebaceous cysts behind the ear, which are mainly due to the long-term accumulation and storage of sebaceous secretions in the sebaceous glands behind the ear due to blocked secretion. If there is an osteoma of the mastoid process, this condition may also manifest itself. In conclusion, if a patient has a hard lump behind the ear, it is recommended that the patient improve the local examination, the ultrasound examination of the neck behind the ear, and if necessary, the CT or MRI examination.