Outsourcing support activities in companies and industries is a key trend with core business strategy. This trend has increased with the hardening of the current financial crisis. The issue of outsourcing support is a major theme in the field of risk prevention. Even if, outsourcing is considered by Preventers as a key factor of risk, Managers still consider this solution as cost-effective and in some cases that subcontractors have more expertise. This paper will report on a methodology developed for studying the risks (financial, judicial, availability, safety) induced by outsourcing and the conclusion of a real case study performed in 2009 within a company submitted to authorization in order to optimize the management of outsourcing contracts. We will first analyze the state of the art about risks and benefits induced by outsourcing. A description of the company and the management's request will be described in a second time. We will then present our comprehensive methodological approach based on decision aiding framework and on the achievement of an organizational diagnosis to consider impact on working relationships and organizational conditions in managing outsourcing service delivery contracts. Finally, we will discuss the way our recommendations were taken into account by the management staff more than two years after proposing an action plan aiming at sustaining the quality and the performances of the services delivered to the Companies