Medication discrepancies remain common at hospital discharge, despite intense efforts to improve medication reconciliation processes. Conducted in a geriatric patient population, this prospective cohort study found a similar incidence of medication discrepancies at discharge compared with prior studies, but concerningly, patients were unaware of most of these errors. Both provider errors and patient misunderstanding occurred more frequently for medications prescribed for conditions other than the primary hospital diagnosis, indicating that disease-specific efforts to improve medication safety may miss many errors.