The system presented in this paper proposes to implement the concept of evidence-based medical practice. This reasoning framework permits physicians to associate preferences to the kind of knowledge they reuse during their care, favoring knowledge based upon more evidence. This system is a computerized decision-support assistant for the long-term follow-up of bone-marrow post-transplant care. It manages the cooperation of case-based reasoning, rule-based reasoning and knowledge acquisition to solve patient problems. In this domain, no knowledge source alone can address the range of problems met, and the cooperation of the different knowledge sources, such as cases, pathways and guidelines, provides a much better coverage of both the variety and complexity of the different problems to solve.