As patient's medical data is disseminated in different health structures, developing a medical or epidemiological patient-oriented data warehouse has some specific requirements compared to intra healthcare structure datawarehousing projects. The difference is that the healthcare structures implicated in a patient-oriented data warehouse project require some considerations about the confidentiality of the patient data and of the activities of healthcare structures.

Building a data-warehousing system at a regional level, for example in cancerology, requires the participation of all concerned health structures, as well as different health professionals. The heterogeneity of sources medical data of has to be taken into account for choosing between several organizational configurations of the data warehousing system.

In top of data warehousing, we propose a concept of Virtual Intranet, which provides a solution to the problem of medical information security arising from heterogeneous sources.