The Institute of Medicine highlighted the challenges of health information technology implementation in their 2011 report, Health IT and Patient Safety. A growing list of unintended consequences from computerized provider order entry (CPOE) systems has emerged over the last few years. This study describes a robust classification structure for identifying systems-related errors in CPOE programs. Two hospitals with different CPOE systems were examined. Systems-related errors were found to be frequent, comprising 42% of all prescribing errors, although only 2.2% were serious errors. Both CPOE systems in this study prevented many more prescribing errors than they created, supporting the overall benefit of CPOE for patient safety. An AHRQ WebM&M perspective discussed CPOE and medication safety.