PURPOSE: There has been considerable effort in recent years to link and integrate professional services more closely for patients with comorbidities. However, difficulties persist, especially at the clinical level. This study aims to shed light on these difficulties by examining the process of sensemaking in professionals directly involved in this integration. DESIGN/METHODOLOGY/APPROACH: The authors conducted an eight-year longitudinal case study of an organization specializing in mental health and substance abuse. Different data collection methods were used, including 34 interviews conducted between 2003 and 2009, observations and document analysis. The authors performed a qualitative analysis of the data using a processual perspective. FINDINGS: This paper provides empirical insights about the nature of the sensemaking process in which professionals collectively participate and the effects of this process on the evolution of integrated services. It suggests that the development of integrated practices results from an evolutional and collective process of constructing meanings that is rooted in the work activities of the professionals involved. PRACTICAL IMPLICATIONS: By drawing attention to the capacity of professionals to shape the projects they are implementing, this study questions the capacity of managers to actually manage such a process. In order to obtain the expected benefits of integration projects, such emergent dynamics must first be recognized and then supported. Only then can thought be given to mastering them. RESEARCH LIMITATIONS/IMPLICATIONS: The fact that this is a single case study is not a limitation per se, although it does raise the issue of the transferability of results. Replicating the study in other contexts would verify the applicability of the authors' conclusions. ORIGINALITY/VALUE: This study offers a fresh perspective on the difficulties generally encountered at the clinical level when trying to integrate services. It makes a significant contribution to work on the dynamics of sensemaking in organizational life.