On March 11, 2011, the Great East Japan Earthquake and ensuing tsunami that hit the northeastern coastal region of Japan caused about 18,000 casualties and destroyed numerous buildings. Additionally, many medical facilities were damaged and patient medical records lost. In order to maintain patient clinical information, a prefectural medical network system, the Miyagi Medical and Welfare Information Network (MMWIN), began providing backup data storage services in 2013 for hospitals, clinics, pharmacies, and other care facilities as a precaution for upcoming disasters. This system also facilitates the sharing of clinical information trans-institutionally as long as patients provide consent for this. In the present study, we examined the development of the MMWIN and its efficiency during the 5 years from its launch, and identified general problems to maintain such a backup system. At the end of 2018, the system contained backup data from more than 11 million patients with more than 420 million data items; more than 900 facilities were MMWIN users, and the number of patients consenting to sharing their clinical information reached 90,000. The use of the system has become widespread and the accumulating data should be utilized for research in the future. Maintaining a balance between income and cost is critical to make this project independent from local government subsidies.