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Studies have shown that temperature at the extremes of the thermoregulatory physiological range, commensurate with a clinical diagnosis of hypothermia (at the lower end) and hyperthermia or fever (at the upper end) increase the risk of a poor neurological outcome and contribute to higher mortality. The tissue most at risk is nervous tissue. That said however, precise measurement of cerebral tissue temperature is seldom made during routine clinical care. More commonly, brain temperature is estimated from measurements of core body temperature. Different measurement sites are frequently used as a proxy or ‘surrogate’ for brain temperature. Knowing whether the assumption that brain temperature can be reliably represented by core body temperature is important because it will help healthcare professionals to deliver appropriate treatment when a rise (or fall) in brain temperature beyond the ‘normal’ range is suspected.This systematic review focused on whether brain temperature is higher, lower, or the same as core body temperature in patients with severe traumatic brain injury.Types of participantsThis review considered studies that include male and female patients, aged 15 years and above, admitted to an adult Intensive Care Unit, with the diagnosis of severe traumatic brain injury, with a Glasgow Coma Scale score of less than eight, and who require brain temperature monitoring.Phenomenon of interestThe review considered studies that measured brain temperature and core body temperature.Types of outcomesThe agreement of core body temperature as a surrogate measure for brain temperature in adult patients with severe traumatic brain injury.Types of studiesThe review considered any randomised controlled trials. In the absence of randomised controlled trials, other research designs such as non-randomised controlled trials, before and after studies, cohort studies, case-control studies and descriptive studies were considered for inclusion.Utilising a three-step search strategy, articles published in English from the years 1980 to 2010 from the following databases were searched: CINAHL, PubMed, Scopus, Web of Science, Science Direct, Ovid SP, Mednar and ProQuest Dissertations & Theses Database.Two reviewers independently reviewed studies using the appraisal tool developed by the authors, as the critical appraisal instrument provided by the Joanna Briggs Institute was not suitable for this systematic review.Data were extracted using the extraction tool developed by the authors, as the data extraction instrument provided by the Joanna Briggs Institute was not suitable for this systematic review.A narrative summary of all findings was presented as statistical pooling was not possible.Thirty-three studies were identified through the keywords search using the databases listed above. Eight studies were included in this systematic review after the assessment of methodological quality. Eleven temperature comparisons were identified in eight studies. Most comparison showed brain temperature to be higher than core body temperature. However, three studies showed core temperature being higher than brain temperature, especially when patients' brain temperature dropped below 36°C.Brain temperature cannot be predicted by core body temperature. None of the core body temperature sites included in this review can be a surrogate for brain temperature. Concurrent monitoring of brain and body temperature is important in managing patients with severe traumatic brain injury.As body temperature does not accurately reflect brain temperature, brain temperature and core temperature should be monitored concurrently in patients with severe traumatic brain injury who are admitted to the Intensive Care Unit.Future studies should focus on having larger sample sizes and standardised brain and core temperature measurement sites.