Case-Based Reasoning (CBR) as a methodology for Medical Decision Support Systems (MDSS) is considered. This paper proposes a new possibilistic retrieval approach, in which the use of main aspects of possibility theory is proposed for the medical case representation and the definition of the similarity between cases. The performance evaluation of the proposed retrieval approach is conducted using an Endoscopic Case Base. Obtained results confirm that the proposed approach constitutes an efficient tool in terms of medical case representation and possibilistic diagnostic reasoning.