Assertive community treatment (ACT) case managers provide healthcare services to people with severe and persistent mental illness. These case managers take on generic roles in multidisciplinary teams and provide all-around services in the clients’ private homes. This focus group study aimed to gain insight into Danish ACT case managers’ professional identity work by examining their discussions of ethical dilemmas and collaboration in their everyday practice. Data were collected during five focus groups at three ACT teams in the North Denmark Region and subjected to discourse analysis emphasizing how identity work was accomplished through talk. The findings indicated that the case managers constructed professional identities by actively positioning themselves and the particular ACT approach in relation to other mental healthcare professionals and clients. They represented themselves as achieving better client-related outcomes by being more assertive and persistent, and as responsible caregivers who provided the help that their clients needed when other services had failed to do so. They depicted their services as being focused on the clients’ well-being, and their persistent efforts to establish and sustain interpersonal relationships with clients were an important part of their service. Basic nursing tasks were described as an important part of their everyday work, and even though such tasks were not distinctive for ACT case managers, the representations of their work seemed to give them a sense of worth as professionals and legitimized a unique role in the community mental healthcare services.