['This study sought to evaluate the effectiveness of an active survey method for detecting anesthesia nonroutine events (NREs). An NRE is any aspect of clinical care perceived by clinicians or observers as a deviation from optimal care based on the context of the clinical situation.', "A Comprehensive Open-ended Nonroutine Event Survey (CONES) was developed to elicit NREs. CONES, which consisted of multiple brief open-ended questions, was administered to anesthesia providers in the postanesthesia care unit. CONES data were compared with those from the same hospital's anesthesia quality assurance (QA) process, which relied on self-reporting of predefined adverse events.", 'CONES interviews were conducted after 183 cases of varying patient, anesthesia, and surgical complexity. Fifty-five cases had at least one NRE (30.4% incidence). During the same 30-month period, the QA process captured 159 cases with 96.8% containing at least one NRE among the 8,303 anesthetic procedures conducted (1.9% overall incidence). The CONES data were more representative of the overall surgical population. There were significant differences in NRE incidence (P < 0.001), patient impact (74.5% vs. 96.2%; P < 0.001), and injury (23.6% vs. 60.3%) between CONES and QA data. Outcomes were more severe in the QA group (P < 0.001). Extrapolation of the CONES data suggested a significantly higher overall incidence of anesthesia-related patient injury (7.7% vs. only 1.0% with the QA method).'] Does a facilitated survey instrument capture significantly more anesthesia events than does traditional voluntary event reporting?