Although medication reconciliation is a common strategy to improve medication safety, barriers to implementation and threats to safety persist. Based on events reported to the Pennsylvania Patient Safety Reporting System, the authors characterized serious events related to medication reconciliation. The most common process failures contributing to patient harm occurred during order entry/transcription and resulted most frequently in the wrong dose or dose omission. The authors suggest risk reduction strategies including defined clinician roles for medication reconciliation, listing the indication for prescribed medications, and adding anticonvulsants to processes for medication with high risk for harm.