Medication errors and adverse drug events (ADE) are unfortunately common at hospital discharge. This study used the National Reporting and Learning System (NRLS) in England and Wales to identify contributing causes to medication errors and ADE. Patients over 65 were the most common age group and, of incidents with a stated level of harm, most did not result in any harm. Overall, most incidents occurred at the prescribing stage, but varied by patient age group. Most contributory factors were organizational (e.g., continuity of care between provider types), followed by staff, patient, and equipment factors.