This study compared three information sources for medication reconciliation: an individual pharmacist-compiled medication history (which is quite labor intensive to collect), the medications in the electronic health record, and medication data from pharmacy insurance claims. The information provided from electronic health records and the insurance claims matched the gold-standard pharmacist medication history about half the time; combining them increased the odds of obtaining a correct medication list. This finding suggests that it may be possible to use available data, such as that found in electronic health records and insurance claims, to enhance medication reconciliation practice.