Inadvertent perioperative hypothermia, a common occurrence in the operating suite, is associated with many adverse outcomes. It is the nurse anesthetist's goal to attenuate the incidence of this problem. Although active intraoperative warming is a widely accepted practice, active preoperative warming may be a less explored option for temperature maintenance. A search strategy to identify systematic reviews and investigations in peer-reviewed journals was undertaken to identify evidence examining the efficacy of preoperative warming. Evidence sources meeting the search criteria were randomized controlled trials and a cohort study using historical controls. Most of the studies support the implementation of active preoperative warming by demonstrating that subjects were warmer during the perioperative period. Overall, these differences were statistically significant and likely clinically significant. Future clinical trials should examine shorter warming times and lower warming unit settings, should include appropriate sample sizes, and should consistently employ trained staff using calibrated biometric instruments to measure temperature.