The GINSENG (Global Initiative for Sentinel E-health Network on Grid) project aims to implement a grid infrastructure for e-health and epidemiology in Auvergne. A distributed medical database is created upon a secure network for epidemiological studies. Our goal is to create a decentralized information system using grid technologies. The medical sites involved in the project are clustered around two themes: cancer monitoring and perinatal care. On each medical site a server which duplicates the medical database, is deployed with grid services. At the same time, full control of the information is kept by the organizations storing patients' files. This solution allows for a high level of security, privacy, availability, and fault tolerance. Queries made on the distributed medical databases are made via a secure web portal. Public health authorities use this infrastructure for health monitoring, epidemiological studies and evaluation of specific medical practices.