and treatment.Fever Without Source in Children 0 to 36 Months of Age

[10–12] warrants using the current outpatient reference standard, rectal ther-mometry, when measuring temperatures in young children. An accurate tempera-ture measurement is especially important if a practitioner chooses to use feverDefinition of fever A variety of temperatures have been used to define fever, but the most commonly accepted definition of fever is a temperature of 38.08C (100.48F), a value derived from studies by Wunderlich, who took 1 million measurements on 25,000 patients and determined that this temperature was the upper limit of normal [9]. Although less invasive means of measuring temperature exist, such as axillary and aural thermometry, the variability of measurements at these sitesFever, one of the most common chief complaints of children seeking medical attention [1,2], prompted over 5 million emergency department (ED) visits in 2002 [3]. Most of these children have identifiable causes of their fevers, but many will have fever without an apparent source (FWS) after conclusion of the history and physical examination. Despite the frequency of fever as a chief complaint, there is considerable controversy in the management of the young child who has FWS [4–8]. The challenge in the evaluation of the febrile young child lies in balancing the minimization of risk to the patient with the costs of testin