Chronic diseases are increasing rapidly and this phenomenon is becoming a major burden to the health delivery system around the world. A new health care paradigm with focus on chronic treatment and care will actualize the need for interoperable standards based services due to the complexity of care where different health levels and professions are involved. Given the complexity of the domain, we argue the need for a systematic and formal approach to the development of interoperable information systems if there shall be any real support of the cooperating actors. We describe our work on technical interoperability done in the Linkcare project addressing new models of care and technology to support them in the domain of the chronically ill using concrete results from an architecture built using the MAFIIA architecture framework and the UML 2.0 profile for software services, and argue that building formal architectural descriptions on the basis of shared interface descriptions and profiles are an important part of achieving continuity of care based on sustainable health systems.