The purpose of this paper is to identify the factors that contribute to a successful long-term outsourcing arrangement, particularly in the facilities management area. Organisations expect to achieve many benefits from outsourcing, despite the fact that there are significant risks associated with unsuccessful outsourcing. The paper analyses a successful multiple activity outsourcing case study. Six managers and team leaders, who have initiated and managed the sixteen outsourced activities during an eight year period, were interviewed. In order to complement and confirm the interviews, the observation of four monthly performance review meetings was conducted. Eighteen key success factors for a long-term outsourcing arrangement have been identified and approved by the interviewees. They have been used to construct the 18C's model.