This thesis is a case study of the informal internal communication at a Swedish government agency called Swedac. The purpose of the study was to investigate how the employees perceive and use the informal internal communication, what communication media they utilize for it and how the informal internal communication correlates to certain aspects of the organizational structure. In order to achieve this, six qualitative interviews was carried out with employees in the organization. Since informal internal communication is not a well-defined concept I explained my view of the concept in the thesis. The results show that the informal internal communication is very important and fairly widespread at Swedac. One of the main qualities with informal internal communication seems to be its quickness. Mainly three different types of communication media were used – face-to-face, telephone and email. The organizational structure and the informal internal communication correlate in many interesting ways. For example, most of the informal internal communication takes place inside formal work units. The main conclusion is that the informal internal communication supports the organization quite well.