The development of healthcare systems in accordance to the “Shared Care” paradigm results in co-operative health information systems across the boundaries of organisational, technological, and policy domains. Increasingly, these distributed and heterogeneous systems are based on middleware approaches, such as CORBA. Regarding the sensitivity of personal and medical data, such open, distributed, and heterogeneous health information systems demand a high level of data protection and data security, both with respect to patient information and with respect to users. The security concepts and measures available and additionally needed in health information systems based on CORBA architecture are described in this paper. The proposed security solution is also open to other middleware approaches, such as DHE or HL7.