This paper reports an experience of computerising a clinical guideline for the management of non-insulin-dependent diabetes mellitus (NIDDM). The guideline, designed by the European NIDDM Policy Group is being used in a National Programme for Diabetes supported by the Portuguese Ministry of Health, who is keen to supporting its widespread use by general practitioners, namely in computerised form. The paper presents the main characteristics of the prototype that was implemented within the European project Prestige, and was developed according to the Prestige Protocol Model. The model is briefly described, together with the generic architecture that supports it. Then the main design decisions of the prototype are explained, regarding the modelling of a general practitioner workflow during a typical consultation and the user interface, two key issues for obtaining acceptance from the users. The limitations of the system are discussed and a number of directions are outlined in order to circumvent such limitations, and broaden the scope of applicability of the system.