Despite the recognized benefits of electronic medical records and electronic health care data, many organizations have not implemented such a system. The cost of licensing proprietary systems and customizing them to meet an organization’s needs are major barriers. Other barriers include great uncertainty about the chosen system continuing to be best for the organization, whether the new system will integrate with their existing IT systems, and whether it will remain viable over time and as technology changes. Many of these problems can be addressed through the use of open source software (OSS). OSS computer code is free and available for download by anyone. There are no license fees for OSS and the software can be freely modified by an organization to its specific needs. In addition, OSS-based medical record systems are attractive to medical organizations because they offer the ability to avoid a ‘lock-in’ state. At present there are more than 150 health-related OSS projects, some of which have achieved worldwide distribution and use. Implementing electronic record keeping in Japan presents similar barriers, namely high costs, organizational inflexibility, and restrictions associated with implementing proprietary software systems. To address these barriers, the Japan Medical Association has developed and made available an OSS-based information and communication infrastructure. The project is called ORCA, for Online Receipt Computer Advantage. Today, more than 14,000 medical providers in Japan are using computer products from the ORCA project. In this article, we address the use of OSS in Japan’s health care system.