To study the detrimental effects of operating room noise, noise levels in operating rooms were first measured and the average noise level was calculated in Decibels, which was 77.32 dB(A). An audiocassette of 90 min duration was prepared recording the operating room noise. The same audiocassette was used later to expose the 20 anaesthesia residents to the operating room noise in the acoustically treated rooms of audiology department. The noise level during exposure was maintained at 77.32 dB(A). Two cognitive functions, mental efficiency and short-term memory were studied. The tests used were the Trail Making Test and Digit Symbol Test for mental efficiency and the Benton Visual Retention Test for short-term memory. The mean pre-exposure scores for the Trail Making Test, Digit Symbol Test and Benton Visual Retention Test were 22.9 +/- 1.94, 83 +/- 2.62 and 9.55 +/- 0.51 respectively. The mean during-exposure scores were 16.35 +/- 1.39, 74.05 +/- 3.46 and 5.8 +/- 0.41 respectively (P < 0.05). In conclusion, we observed that operating room noise reduced the mental efficiency and short-term memory of anaesthesia residents.