This article questions the effectiveness of a managerial tool in changing a health-care system. The process of implementing regional planning and its impact on creating integrated service networks is examined, using a case study and a multi-dimensional analytic model. This model highlights the influence of contextual, structural, cultural and dynamic factors on forming networks. The regional planning developed in the province of Québec (Canada), aimed at a major transformation of the mental health-care system. In each district, organizations working with people who have serious mental disorders were mobilized to plan and implement a more coordinated, continuous and diversified supply of services, under the direction of a regional health body. This study outlines the limitations of regional planning as a tactic for transforming the system. It recommends instead developing more diversified integration strategies to further the process of forming integrated service networks within a complex system. In conclusion, a brief discussion deals with the difficulties related to the study of systemic change implementation.