Hypothesis Surgical operative performance benefits from analysis of the mechanisms underlying technical errors committed during surgery. Design Prospective study using the Observational Clinical Human Reliability Assessment (OCHRA) system and complete unedited videotapes of the operations. Setting Three National Health Service hospitals within the United Kingdom. Patients Two hundred consecutive patients with symptomatic gallstone disease. Interventions Elective laparoscopic cholecystectomy for symptomatic gallstone disease by surgeons, who were blind to the nature and objectives of the study, using their usual operative technique. Main Outcome Measures Surgical consequential and inconsequential operative errors. Results The analysis ...