When dealing with a specific patient case, physicians are often interested in retrieving a personalized version of a clinical guideline, that is a version tailored to their use needs. In a patient-centric scenario, empowered patients make up another class of users interested in retrieving personalized care plans from a guideline repository. In their previous work, the authors proposed techniques to efficiently provide ontology-based personalized access to very large collections of multi-version clinical guidelines. In this paper, they address the problem of also dealing with a multi-version ontology used to support personalized access to clinical guidelines. The authors' approach allows the semantic indexing of guideline contents with respect to multi-version ontology classes and exploits the IS-A relationship among such classes for granting personalized access. Efficiency is ensured by a newly introduced annotation scheme for guidelines and solutions to cope with the evolution of ontology structure. The tests performed on a prototype implementation confirm the goodness of the approach.