 An incomplete understanding of patients preadmission medications and failure to reconcile these with medications ordered in the hospital and at discharge are major, previously unappreciated, causes of adverse drug events ADEs. The Joint Commission for Accreditation of Healthcare Organizations has now mandated a process for reconciling all medications at hospital admission and discharge. The best ways to implement medication reconciliation and the impact on patient outcomes are unknown. We, the researchers at at Brigham and Womens Hospital, will design and implement a medication reconciliation process with two major components: 1 information technology to integrate medication reconciliation into the current workflow at Brigham and Womens Hospital BWH; and 2 process re-design involving physicians, nurses, and pharmacists to ensure that reconciliation takes place. We will then conduct a randomized controlled trial on the General Medical Service of BWH to evaluate the effects of this new process on reducing medication reconciliation errors with the potential to cause patient harm potential ADEs. 