Background: Modern-day health systems are complex, making it difficult to assure continuity of care for older persons with multi-morbidity. One way of intervening in a health system that is leading to fragmented care is by utilising Case Management (CM). CM aims to improve co-ordination of healthcare and social services. To better understand and advance the development of CM, there is a need for additional research that provides rich descriptions of CM in practice. This knowledge is important as there could be unknown mechanisms, contextual or interpersonal, that contribute to the success or failure of a CM intervention. Furthermore, the CM intervention in this study is conducted in the context of the Swedish health system, which prior to this intervention was unfamiliar with this kind of coordinative service. The aim of this study was to explore the everyday work undertaken by case managers within a CM intervention, with a focus on their experiences. Methods: The study design was qualitative and inductive, utilising a focused ethnographic approach. Data collection consisted of participant observations with field notes as well as a group interview and individual interviews with nine case managers, conducted in 2012/2013. The interviews were recorded, transcribed Verbatim and subjected to thematic analysis. Results: An overarching theme emerged from the data: Challenging current professional identity, with Three sub-themes. The sub-themes were 1) Adjusting to familiar work in an unfamiliar role; 2) Striving to improve the health system through a new role; 3) Trust is vital to advocacy. Conclusions: Findings from this study shed some light on the complexity of CM for older persons with multi-morbidity, as seen from the perspective of case managers. The findings illustrate how their everyday work as case managers represents a challenge to their current professional identity. These findings could help to understand and promote the development of CM models aimed at a population of older persons with complex health needs.