Hard stop alerts within computerized provider order entry (CPOE) systems are intended to avert serious medication errors by preventing prescribing of contraindicated medications. This study investigated whether data from a CPOE system could be used to identify individual physicians who commit more frequent prescribing errors. However, the study found that trainee physicians who committed errors prompting hard stop alerts were not more likely to commit less serious prescribing errors, nor did they appear to ignore prescribing warnings more frequently. Although objective performance data would help identify doctors who frequently make prescribing errors, this study's results indicate that triggering of CPOE alerts is not a reliable measure.