The purpose of this study was to investigate how communication within the Swedish sickness insurance system differs between cases of sick leave and how this may affect clients' cases. This was a document study using 30 client files from the Swedish Social Insurance Agency (SIA). The clients included had been on a work ability evaluation during their sick leave spell and were aged 32-64 years. The material was analyzed using qualitative document analysis. The results show different approaches to communication, characterized by emotional argumentation, matter-of-fact driven argumentation and information exchange, which have diverse success in affecting official decisions. Arguments characterized by emotions such as frustration or desperation are to a larger extent neglected by the authorities compared to those characterized by a matter-of-fact driven approach and referring to regulations and medical certificates. There are differences regarding how clients and stakeholders communicate the clients' needs and pre-requisites, and how this affects official decisions. Further research must be carried out in order to establish social insurance literacy, initially for individuals on sick leave within the sickness insurance system, and whether there are differences between diverse groups that could lead to injustices.Implications for rehabilitationWithin a social insurance context, professionals need to provide clients with adequate and individually adapted information in order for procedures to be perceived as comprehensible and manageable by the clients.The support from stakeholders such as the treating physician and/or employer can affect clients' sick-leave process.Clients' treating medical professionals can contribute to ensuring that clients rights are met by communicating the clients' needs to other stakeholders in a formal way.