Medication reconciliation continues to pose significant threats to patients when they transition in and out of the hospital setting. This study found that reconciliation errors occurred frequently at both these transition times; 42% of patients had at least one error in their preadmission medication list (PAML). Clinically relevant PAML and admission order errors were associated with older age and the number of preadmission medications. These errors were less likely when a recent medication list was available in the electronic health record. Discharge medication errors were more likely for every PAML error and the number of medication changes during hospitalization. A past AHRQ WebM&M commentary discussed a medication reconciliation victory after an avoidable error.