The ARTEMIS project is developing a semantic web service based P2P interoperability infrastructure for healthcare information systems. The strict legislative framework in which these systems are deployed means that the interoperability of security and privacy mechanisms is an important requirement in supporting communication of electronic healthcare records across organisation boundaries. In ARTEMIS, healthcare providers define semantically annotated security and privacy policies for web services based on organisational requirements. The ARTEMIS mediator uses these semantic web service descriptions to broker between organisational policies by reasoning over security and clinical concept ontologies.