We demonstrate the integration of a longitudinal, internally-developed legacy clinical information system with a vendor-based electronic health record application. The expense of developing the interface across systems was minimal, and it was successfully incorporated within the vendor EHR. Users consistently used the legacy data view while using the EHR; usage reached up to 50% of accessed data. Data showing concurrent increases in the use of the legacy data view and adoption of the new EHR suggests the method may improve adoption of the new system.