BACKGROUND: Numerous electronic devices have been introduced into operating rooms. Although little is known about the relationship between exposure to electromagnetic fields and health hazards, several studies have demonstrated causal relationships between electromagnetic fields exposure and various symptoms, cancers, and other diseases. METHODS: This study was approved by the Institutional Review Board. The intensity of extremely low-frequency electromagnetic fields was measured during surgery with the extremely low-frequency electromagnetic field strength measurement system at the standing position of anesthesiologists in 18 operating rooms and analyzed with EMDEX analysis and graphical program (EMCALC 95; ENERTECH, Campbell, CA). RESULTS: The average measurement duration per operating room per day was 7.41 +/- 0.70 h (mean +/- SD). The average sample number of measurements was 888.11 +/- 82.75 per operating room. The average magnetic field was 5.83 +/- 5.23 milliGuass (mG) (range, 0.10-33.80 mG), with 70% of these levels 2 mG or greater. CONCLUSIONS: The authors' results indicate that anesthesiologists in operating rooms are exposed to extremely low-frequency electromagnetic field levels that exceed magnetic field intensity of 2 mG recommended by the Swedish Board for Technical Accreditation for production by computer monitors and detected 30 cm from them. It currently is not clear if this exposure has health effects on anesthesiologists and other operating room personnel.