BACKGROUND Door openings and increased foot traffic in operating rooms (ORs) during total joint arthroplasty are thought to increase the risk of surgical site infection. METHODS Digital manometers were used to collect pressure data during off-hours at the thresholds of both the outer door (ie, the door to the common OR hallway) and the inner substerile door, which opens to the substerile hallway, of six empty ORs used for total joint arthroplasty. Airflow patterns were visualized with smoke studies to determine whether outside air entered the ORs during single or multiple door openings. Data were analyzed using the Student t-test and one-way analysis of variance. RESULTS Positive pressure was not defeated during any door-opening event. The average time for recovery of the initial pressurization in the OR regardless of the door used was between 14 and 15 seconds (P = 0.462). No differences in the degree of room depressurization were noted between entry of personnel through the outer door, passing of a surgical tray through the outer door, and entry of personnel through the inner door (P = 0.312). Smoke studies confirmed that no contaminated outside air entered the OR with single door opening. Outside air entered the OR if two doors were open simultaneously. CONCLUSIONS Single door opening does not defeat OR positive pressure, but simultaneous opening of two doors allows contaminated air to flow into the OR. OR traffic should continue to be limited during surgical procedures. OR personnel should be educated about the danger to the sterile field that can result from simultaneous door openings and should be discouraged from such activity.