Fever is one of the most frequent signs seen in children at consultation. In infants under the age of 3 months, fever is nonspecific and is often the only sign of a potentially severe infection. It has been estimated that two-thirds of the children hospitalized have a viral infection and 10% a bacterial infection with risks of complications including meningitis. It must be recalled that 5% of the infants with septicaemia due to Haemophilus influenzae b who does not receive an appropriate treatment will develop meningitis or another focal infection. There is agreement on the definition of potentially severe infections: meningitis, osteoarthritis, cellulitis or cellulodermitis, urinary infection, lung infection and gastroenteritis. Certain authors also include inner ear infections. In suspected cases, the need for hospitalization can be based on signs of impaired consciousness and/or muscle tone, abnormal heart rate, blood pressure or recoloration time, paleness, cyanosis, respiratory distress, signs of dehydration, or abnormal behaviour. In order to identify infants at low risk, in addition to the physical examination, the clinician can rely on essential laboratory tests: white cell count with differential count, blood culture, C-reactive protein and/or sedimentation rate with fibrinogen and an urinanalysis. A chest X-ray is required in case of respiratory signs and a culture of the fecal matter is needed in case of diarrhoea. On the basis of these findings and the clinical picture, if the criteria of low risk of bacterial infection are fulfilled in an infant under 3 months of age with fever, most authors agree that a spinal tap must nevertheless be performed. When these tests lead to the conclusion of low risk, close surveillance at home is appropriate. If the clinical picture worsens within 24h hospitalization is required.