While significant literature exists on hospital-based "code calls," there is a lack of research on calls for help in the operating room (OR). The purpose of this study was to quantify the rate and nature of calls for help in the OR of a tertiary care hospital. For a 1-year period, all calls were recorded in the main OR at The University of California, Irvine Medical Center. The average rate of calls per 1000 anesthesia hours was 1.4 (95% CI, 1.1-1.8), corresponding to a rate of 5.0 (3.8-6.5) calls per 1000 cases. Airway (44%), cardiac (32%), and hemorrhagic (11%) emergencies were the most common etiologies. Thirty-day mortality approached 11% for patients who required a call for help in the OR.