The aim of this study was to examine the social service employees, from the substance abuse section, experiences of the collaboration between them and the adult psychiatric facilities within Malmö stad when they encounter clients with co-occurring substance abuse and mental health problems and therefore share the responsibility. The aim is also to examine what kind of responsibility the social service employees feel they have regarding the mental health problems when they encounter clients with co-occurring substance abuse and mental health problems. The study relies on qualitative, semi structured interviews with four employees from the social service substance abuse sections in Malmö stad. The theoretical frame that I based this study on consists of theories regarding collaboration and the new institutional theory. I have also used previous research to gain a deeper understanding and different perspectives of the subject. The result of the study shows that the employees experiences of collaboration is that Malmö stad have some tools that helps them gain a better collaboration with the adult psychiatric facilities, such as the project Integrerad verksamhet, but due to the fact that they belong to two different organizations and therefore have different expectations, rules and cultures, there are still many obstacles in achieving a successful collaboration between the two, especially in the more complex cases of comorbidity. The result also shows that the employees feel responsible for their client's mental health problems, when they encounter clients with co-occurring substance abuse and mental health problems, in the sense that they always investigate if there is a mental illness and start a collaboration with the psychiatric care if they see it necessary. But we can also see that there is some uncertainty regarding what amount of responsibility that lays on a personal level and what is linked to their work assignment