This paper describes the design and implementation of an e-Health authentication architecture using smartcards and a PKI. This architecture was developed to authenticate e-Health Professionals accessing the RTS (Rede Telemática da Saúde), a regional platform for sharing clinical data among a set of affiliated health institutions. The architecture had to accommodate specific RTS requirements, namely the security of Professionals’ credentials, the mobility of Professionals, and the scalability to accommodate new health institutions. The adopted solution uses short-lived certificates and cross-certification agreements between RTS and e-Health institutions for authenticating Professionals accessing the RTS. These certificates carry as well the Professional’s role at their home institution for role-based authorization. Trust agreements between e-Health institutions and RTS are necessary in order to make the certificates recognized by the RTS. As a proof of concept, a prototype was implemented with Windows technology. The presented authentication architecture is intended to be applied to other medical telematic systems.