A major limiting factor in the acceptability of interactive guideline and decision support systems is the ease of use of the system in the clinic. A way to reduce demands upon users and increase flexibility of the interface is to use natural language dialogues and speech based interfaces. This paper describes a voice-based data capture and decision support system in which knowledge of underlying task structure (a medical guideline) and domain knowledge (disease ontologies and semantic dictionaries) are integrated with dialogue models based on conversational game theory resulting in a flexible and configurable interface.