The development of pervasive healthcare systems consist on applying the ubiquitous computing in the healthcare context. The systems developed in this research field have the goals of offering better healthcare services, promoting well-being of the people and assist healthcare professionals in their tasks. The aim of the present work is to give an overview of the main research efforts in the area of pervasive healthcare systems, and to identify which are the main research challenges in this topic of research. Furthermore, we review the current state of the art for these kind of systems with respect some of the research challenges identified. In particular we focus on contributions done into interoperability, scalability and security of these systems.