Urinary tract infection in the first month of life may be revealed by isolated fever, poor weight gain or severe sepsis. It is more frequent in male infants. Escherichia coli is the most common infecting agent. A urinary tract malformation is found in approximately 30% of the cases. In most cases intravenous treatment with an association of cephalosporin and aminoside is efficient. However, because of the possible involvement of an enterococcus, amoxicillin must be added until the result of the urine culture is available. Prophylaxis with oral administration of antibiotics is recommended in case of urinary tract malformation.