The aim of this study was to comprehend and explain the idea and function of Case Management and its diffusion in Swedish municipalities. More specifically its aim was to investigate factors for the diffusion of Case Management and its differences to similar professional roles. The study was based on interviews with four managers at various levels and two case managers representing two municipalities in Sweden. Five themes were identified that were especially interesting when discussing the function of Case Management, its differences to similar professional roles and its diffusion in Swedish municipalities. The themes were: shortcomings in the welfare system, the functions of Case Management, differences to similar professional roles, descriptions of Case Management and factors for the diffusion. The analysis was based on organizational institutionalism and translation, as well as previous research on Case Management and the diffusion of ideas. As a conclusion Case Management was described as a revolutionizing method that would import evidence based social work in the organization. That, and the obvious effort to adapt and integrate Case Management in the institutionalized metods and values of Swedish welfare organizations were factors for the diffusion. Case Management also turned out to be a similar method to the already established profession personligt ombud, wherefor Case Management can be seen as a relaunch of personligt ombud.