Objective:To verify the correlation between temperature measurements performed using an infrared tympanic thermometer and an esophageal thermometer during the intraoperative period. Method: A longitudinal study of repeated measures was performed including subjects aged 18 years or older undergoing elective oncologic surgery of the digestive system, with anesthesia duration of at least 1 hour. Temperature measurements were performed simultaneously by a calibrated esophageal thermometer and by a calibrated infrared tympanic thermometer, with laboratory reading precision of ±0.2°C. The operating room temperature remained between 19 and 21°C. Results: The study included 51 patients, mostly men (51%), white (80.4%). All patients were kept warm by a forced-air heating system, for an average of 264.14 minutes (SD = 87.7). The two temperature measurements showed no different behavior over time (p = 0.2205), however, tympanic measurements were consistently 1.24°C lower (p<0.0001). Conclusion: The tympanic thermometer presented reliable results but reflected lower temperatures than the esophageal thermometer. DESCRIPTORS