Developed and experimented at the Service d'Oncologie Médicale Pitié-Salpêtrière (Paris, France) as a computer-based breast cancer guideline system, OncoDoc has already proven to improve physicians' compliance. The underlying methodology relies on a decision-tree knowledge base that the clinician interprets in the context of an actual patient. In order to test whether the implemented strategy and the encoded knowledge base could be reused and shared in another institution, we have experimented the system at the Institut Gustave Roussy with only minor but legitimate customizations. For each patient, clinicians had to record their a priori therapeutic attitude, to use the system, to evaluate the system, and to record their final decision. Adherence (79%) and compliance (88%) rates were even higher than those previously observed. In addition, the approach appeared to influence clinicians' behavior—16% of initial decisions were changed to comply with recommendations—and to increase clinical trial accrual (+50%).