Duplication of medical testing results in a financial burden to the healthcare system. Authors undertook a retrospective review of duplicate testing on patients receiving coordinated care across two institutions, each with its own electronic medical record system. In order to determine whether duplicate testing occurred and if such testing was clinically indicated, authors analyzed records of 85 patients transferred from one site to the other between January 1, 2006 and December 31, 2007. Duplication of testing (repeat within 12 hours) was found in 32% of the cases examined; 20% of cases had at least one duplicate test not clinically indicated. While previous studies document that inaccessibility of paper records leads to duplicate testing when patients are transferred between care facilities, the current study suggests that incomplete electronic record transfer among incompatible electronic medical record systems can also lead to potentially costly duplicate testing behaviors. The authors believe that interoperable systems with integrated decision support could assist in minimizing duplication of testing at time of patient transfers.