In this article we propose an approach for a decision support system (DSS) based on Knowledge Discovery from Databases (KDD). In such system, user must be involved throughout the decision-making process. In consequence we propose the integration of a Human–Computer Interaction (HCI) model into the development of DSS process based on KDD. The approach we propose is based on two systems development methods—the Unified Process (UP) from Software Engineering and the U model from HCI. In this article, we describe our combined approach (UP/U) and the way we used it to develop a DSS in a medical field.