As computerized health-care support systems are rapidly becoming more knowledge intensive, the representation of medical knowledge in a form that enables reasoning is growing in relevance and taking a more central role in the area of Medical Informatics. In order to achieve a successful decision-support and knowledge management approach to medical knowledge representation, the scientific community has to provide efficient representations, technologies, and tools to integrate all the important elements that health care providers work with: electronic health records and health care information systems, clinical practice guidelines and standardized medical technologies, codification standards, etc. Synergies to integrate the above mentioned elements and types of knowledge must be sought both in the medical problems (e.g., prevention, diagnosis, therapy, prognosis, etc.) and also in the Computer Science and Artificial Intelligence technologies (e.g., natural language processing, digital libraries, knowledge representation, knowledge integration and merging, decision support systems, machine learning, e-learning, etc.). The sixth international KR4HC workshop will aim at attracting the interest of novel research and advances contributing in the definition, representation and exploitation of health care knowledge in medical informatics. Both well-founded theoretical works and applications are welcome. Historical Remark of the Workshop: The first KR4HC workshop , held in conjunction with the 12th Artificial Intelligence in Medicine conference (AIME’09), brought together members of two existing communities: the clinical guidelines and protocols community, who held a line of four workshops (European Workshop on Computerized Guidelines and Protocols CPG’2000 and CPG’2004; AI Techniques in Health Care: Evidence-based Guidelines and Protocols 2006; Computer-based Clinical Guidelines and Protocols 2008), and a related community who held a series of three workshops devoted to the formalization, organization, and deployment of procedural knowledge in health care (CBMS’07 Special Track on Machine Learning and Management of Health Care Procedural Knowledge 2007; From Medical Knowledge to Global Health Care 2007; Knowledge Management for Health Care Procedures 2008). Since then, two more KR4HC workshops have been held KR4HC'10 and KR4HC'11 , in conjunction with the ECAI’10 and the AIME’11 conferences. In 2012, the Forth KR4HC workshop was organized in conjunction with ProHealth as part of the BPM’12 conference. We continuing the efforts that with a second Joint Workshop on Knowledge Representation for Health Care and Process-Oriented Information Systems in Health Care (KR4HC/ProHealth) in the 14th Artificial Intelligence in Medicine conference (AIME’13). This year, the Sixth International Workshop on Knowledge Representation for Heath Care is organized together with the KR'14 conference within the Vienna Summer of Logic.