This study reports the findings from interviews with 139 anesthesiologists, residents, and nurse-anesthetists about their observation of errors. The authors describe characteristics from more than 1000 incidents collected and offer strategies to both detect and prevent future ones. Based on the patterns noted, the discussion suggests that human error played a dominant role in the reported incidents. The authors conclude that it may be beneficial to classify specific incidents by a preventive strategy, rather than one based on outcomes, in order to prevent future adverse events and provide more constructive learning from previous errors.