Understanding how users form perceptions of a software innovation would help software designers, implementers and users in their evaluation, selection, implementation and on-going use of software. However, with the exception of some recent work, there is little research examining how a user forms his or her perceptions of an innovation over time. To address this research need, we report on the experiences of a health planner using a DSS software tool for health planning over a 12-month period. Using diffusion theory as outlined by Rogers, we interpret the user's perceptions of the software following Rogers' perceived characteristics of the innovation. Furthermore, we show how our user justifies her attitudes toward the technology using 5 important factors during 3-, 6- and 12-month interviews: stage of adoption, implementation processes, organizational factors, subjective norms, and user competence. Results are compared with key IS research in these areas, and the implications of these findings on the diffusion of decision support systems are discussed.