Hypothesis: Although the risks for operating room distractions and interruptions (ORDIs) are acknowledged, most research on this topic is unrealistic, inconclusive, or methodologically unsound. We hypothesized that realistic ORDIs induce errors in a simulated surgical procedure performed by novice surgeons. Design, Setting, and Participants: Eighteen secondyear, third-year, and research-year surgical residents completed a within-subjects experiment on a laparoscopic virtual reality simulator. Based on 9 months of operating room observations, 4 distractions and 2 interruptions were designed and timed to occur during critical stages in simulated laparoscopic cholecystectomy. The control factor was the absence or presence of ORDIs, with order randomly counterbalanced across the subjects. Main Outcome Measures: The primary outcome measure was surgical errors measured by the simulator as damage to arteries, bile duct, or other organs. The second outcome measure was whether the participants remembered a prospective memory task assigned prior to the procedure and important to operative conduct. Results: Major surgical errors were committed in 8 of 18 simulated procedures (44%) with ORDIs vs only 1 of 18 (6%) without ORDIs (P = .02). Interrupting questions caused the most errors. Sidebar conversations were the next most likely distraction to lead to errors. Ten of 18 participants (56%) forgot the prospective memory task with ORDIs, while 4 of 18 (22%) forgot the task without ORDI (P =.04). All 8 surgical errors with ORDIs occurred after 1 PM (P =.001). Conclusions: Typical ORDIs have the potential to cause operative errors in surgical trainees. This performance deficit was prevalent in the afternoon.