Very little reliable information exists on the sound levels present in an operating room environment. To remedy this situation, sound pressure levels of the operating rooms in Johns Hopkins Hospital were monitored before, during, and after operations. The data were analyzed to determine background sound levels, average equivalent sound levels L(eq), frequency distribution, and peak sound pressure levels L(peak). Each surgery was matched to the period of noise it produced permitting the association of sound levels with particular types of surgeries and the determination of various sound measures for classes of surgery (e.g., orthopedic, neurological, etc.). Averaging over many surgeries, orthopedic surgery was found to have the highest L(eq) at approximately 66 dB(A). Neurosurgery, urology, cardiology, and gastrointestinal surgery followed closely, ranging from 62 to 65 dB(A). By considering the L(peak) along with the L(eq) values, a pattern emerges for the various surgical divisions. Gastrointestinal and thoracic surgery are relatively quiet among the surgical divisions. Neurosurgery and orthopedics have sustained high sound levels. Cardiology surgery has a more moderate average sound level but includes brief periods of extremely high peak sound levels. For neurosurgery and orthopedic surgery, peak levels exceeded 100 dB over 40% of the time. The highest peak levels routinely seen during surgery were well in excess of 120 dB.