Abstract. Clinical guidelines are important means to improve quality of health care while limiting cost and supporting the medical staff. They are written as free text with tables and figures. Transforming them into a formal, computer-processable representation is a difficult task requiring both computer scientist skills and medical knowledge. To bridge this gap, we designed an intermediate representation (or ontology) which serves as a mediator between the original text and different formal guideline representations. It is easier to use than the latter, structures the original prose and helps to spot missing information and contradictions. In this paper we describe the representation and a practical evaluation thereof through the modelling of a real-world clinical guideline.