Fever is a common complaint in paediatric care and is mainly due to infectious causes. Depending on the age of the patient, clinical presentation will differ and the origins of the fever vary ; a good awareness of the age-related specificities is essential for early detection of invasive and potentially fatal infections. Fever may also be due to inflammatory diseases. A good knowledge of these aetiologies is essential to avoid unnecessary repeated antibiotic treatments and a lengthy misdiagnosis.