This paper presents a human-centred design approach for developing Decision Support Systems (DSS) based on a Knowledge Discovery in Databases (KDD) process. The KDD process generates a set of software modules. Our approach is based on a critical study of design methods. It uses the Unified Process (UP), which proposes a general framework; however, the UP does not include enough Human-Computer Interaction (HCI) elements. We suggest enriching the UP activities from the HCI perspective, adding HCI elements. The proposed approach is applied to a KDD-based Dynamic Medical DSS.