Fever up to 39℃ belongs to high fever, whether it is dangerous or not, in addition to the body temperature, we should also combine the patient’s other symptoms, mental state, vital signs, auxiliary examinations, etc. for comprehensive analysis and treatment. Infants and children with fever up to 39℃, with a fair mental state and no other adverse symptoms, are generally not dangerous, and can take oral antipyretic drugs first, pay attention to drinking more water, warm baths, and go to the hospital for blood tests if necessary. If the fever is caused by a simple cold, symptomatic treatment can achieve good results. If the fever is caused by bacterial infection or viral infection, anti-infection treatment is needed. In adults with fever of 39℃, the most common cause is a viral or bacterial infection, which can be treated with physical cooling, oral antipyretics, or anti-infective or antiviral treatment. If the fever is 39℃, accompanied by dizziness, nausea, vomiting, abdominal pain, diarrhea, drowsiness, poor mental status, or even convulsions and other undesirable symptoms, prompt medical attention is needed. Therefore, whether a fever of 39℃ is dangerous or not, it is necessary to systematically analyze according to specific etiology, symptoms, and signs, improve relevant examinations, and actively treat the disease so as not to delay it.