In this paper, a case study is presented in which an early prototype of a decision-support system was integrated in the process of investigating patients with suspected dementia and evaluated. The aims were to capture and model the complex target activity for the purpose of knowledge acquisition and formalization, and qualitatively evaluate the system's compliance with reasoning and work processes as part of the development of a decision-support system for the domain. The results show that contextual factors such as local routines in clinical practice motivate further development of the support integrated in the system for establishing preliminary diagnoses in the investigation process. Keywords. Activity theory, Work analysis, Knowledge-based systems, Decision support, Assessment-Evaluation, Process, Compliance, Human Factors, Cognitive tasks, User-computer interface, Knowledge management, Dementia care