Baby fever for five days can not find the cause of the disease can be caused by hidden parts of the infection, Kawasaki disease, infectious mononucleosis, juvenile idiopathic arthritis, etc., so if the baby fever for five days can not find the cause of the disease, should be combined with the physical examination, improve the relevant tests to clarify the diagnosis. 1. hidden parts of the infection (for example, urinary tract infection, etc.), the child may appear feverish symptoms, but the symptoms of urinary tract irritation is not obvious, which will give the doctor to find the cause of fever brings great difficulties. At this time, the child should complete the urine routine, urine culture and other related tests to clarify the diagnosis. 2. Kawasaki disease is an immune disease, also known as cutaneous mucocutaneous lymph node syndrome, with fever manifesting as high fever, which may be accompanied by rash, conjunctivitis, and enlarged maxillary lymph nodes. Children need to complete physical examination, blood test, immunological examination, cardiac ultrasound and so on in order to make a clear diagnosis. 3. Infectious mononucleosis is an acute infectious disease caused by EBV. There may be fever, pharyngitis, lymph node swelling and other clinical manifestations. It is necessary to improve the blood routine, serum EBV nucleic acid PCR and other tests to clarify the diagnosis. 4. Juvenile idiopathic arthritis, early may be accompanied by high fever, fatigue, loss of appetite and other symptoms, the child needs to improve the relevant examination to clarify the diagnosis. Baby fever for five days can not find the cause of more reasons, it is recommended to improve the relevant examination, combined with clinical examination, after a clear diagnosis to be targeted treatment.