Fever is one of the most frequent reasons for consultation in pediatrics. Despite the progress, the approach of children under 36 months with fever without source of infection is a subject of discussion and a challenge for the pediatrician. While the most frequent cause of the fever is self-limited and of viral etiology, it can also be caused by a severe infection. It is necessary to consider that the risk of serious bacterial infection is higher in younger children and to stress the strategies to identify those children at low risk of developing serious infections to avoid inappropriate use of antibiotics. Urinary tract infection is the most common disease in these children. The most common etiologic agents also change depending on age. The changes in agents related to the incorporation of new vaccines in the national immunization schedule must be taken into account. In order to optimize the use of diagnostic tools, prescriptions of empirical antibiotic therapy and to minimize risks in the care of patients with potential serious bacterial infection, this document was made in order to clarify, in the light of scientific evidence, the management of a child younger than 36 months with fever without apparent focus as an outpatient. It is essential to make an exhaustive and reiterative clinical evaluation in association with laboratory parameters to establish the likely diagnosis and improve the quality of care.