Objective.-Mass participation in competitive open water swimming is becoming increasingly popular. The purpose of this study was to determine whether infrared emission detection (IRED) tympanic temperature measurement taken in participants approximately 1 minute following a long-distance open water swimming event is a suitable screening tool for hypothermia.Methods.-We studied 15 males and 7 females who completed the 20-km Rottnest Channel Swim off the coast of Perth, Western Australia. Following the swim, each athlete was clinically assessed for hypothermia through the observation of gait, cognitive processing, and demeanor. Approximately 1 minute following the swim, participants underwent temperature measurement using one of two IVAC Core Check 2090 IRED tympanic thermometers set to core equivalent mode. Further tympanic readings and an oral temperature reading were taken at 5 minutes post swim in subjects triaged to the medical tent after the initial clinical screen.Results.-At 1 minute post event, the average tympanic temperature measurement was 28.9 degrees C (95% CI. 28.3-29.7). while at 5 minutes postevent it was 31.6 degrees C (95% CI, 31.1-32.2). The average oral temperature at 5 minutes post event was 34.3 degrees C (95% CI, 33.7-34.7). The difference between the screening tympanic and oral temperatures was statistically significant (P = 0.000)Conclusions.-Infrared emission detection tympanic thermometry is unsuitable as a screening tool for hypothermia following a prolonged open water swim because it substantially overestimates the incidence and severity of hypothermia in participants.