This book constitutes the refereed proceedings of the Third International KR4HC 2011 workshop held in conjunction with the 13th Conference on Artificial Intelligence in medicine, AIME 2011, in Bled, Slovenia, in July 2011. The 11 extended papers presented together with 1 invited paper were carefully reviewed and selected from 22 submissions. The papers cover topics like health care knowledge sharing; health process; clinical practice guidelines; and patient records, ontologies, medical costs, and clinical trials.