Background: Since de-institutionalization of psychiatric care (PC) took place in Sweden during the second half of the 20th century, the intended collaboration between the two organizations, PC and community social service (CSS) has been evaluated as inadequate in providing care for persons with long-term mental illness living in the community. Aim: The aim of this explorative study was to examine factors that influence interdisciplinary teamwork between PC and CSSs based on the experience of nursing staff within two separate organizations. Method: Five focus groups were selected as an appropriate method to collect data. Two of these groups were recruited from the PC and three from the CSSs. The focus groups consisted of psychiatric nurses and mental healthcare workers. A qualitative content analysis was used to identify major themes in the data. Findings: Two main themes were found, external organizational factors and interpersonal factors that deter or enhance collaboration between PC and CSS. Separate care plans, unclear times for meetings were found to be a plausible reason for communication failure. The focus groups representing each of the two organizations viewed themselves as ‘us and them’. Different ideologies and goals for caring and service and how to use each other’s competence seemed to be explanations as well as consequences of not finding ways to work together. Conclusion: The results of this study points to the need for the two organizations to find ways to work more effectively together to realize a joint responsibility for the patient/client.