STUDY OBJECTIVE: To assess changes in biological measures of acute stress in surgeons during surgery in real world settings DESIGN: Prospective cohort study SETTING: Tertiary teaching hospital PATIENTS: 8 consultant and 9 training gynecologists INTERVENTION: 161 elective gynecological surgeries of 3 procedures: laparoscopic hysterectomy, laparoscopic excision of endometriosis, or hysteroscopic myomectomy. MEASUREMENTS: Changes in surgeons\' biological measures of acute stress whilst undertaking elective surgery. Salivary cortisol, mean and maximum heart rate (HR) and indices of the heart rate variability (HRV) were recorded prior to and during surgery. MAIN RESULTS: From baseline to during surgery over the cohort, salivary cortisol reduced from 4.1nmol/L to 3.6nmol/L (p鈥?鈥?03), maximum heart rate increased from 101.8 beats per min (bpm) to 106.5bpm (p < .01), root Mean Square of Standard Deviation from 51.1ms to 39.0ms (p < .01) and standard deviation of beat-to-beat variability decreased from 73.7 to 59.8ms (p < .01). Analysis of individual changes in stress by participant-surgery event by paired data graphs reveal inconsistent direction of change in all measures of biological stress despite stratification by surgical experience, role in surgery, level of training, or type of surgery performed. CONCLUSION: This study measured biometric stress changes at both a group and individual level in real world, live surgical settings. Individual changes have not previously been reported and the variable direction of stress change by participant-surgery episode identified in this study demonstrates a problematic interpretation of mean cohort findings previously reported. Results from this study suggest that either live surgery with tight environment control or surgical simulation studies may identify what, if any, biological measures of stress can predict acute stress reactions during surgery.