Context: Some people frequently use healthcare services due to complex healthcare needs and are more at risk of incapacity and mortality. An abundant literature supports case management to improve care integration and outcomes of this clientele. However, challenges remain in the interaction between healthcare centers and primary care clinics. Objective: Implement and evaluate an intervention where primary care nurses work closely with case managers in healthcare centers to improve care integration of frequent users of healthcare services. Study Design: Multiple embedded case study (4 primary care clinic). Setting: Three healthcare centers and four primary care clinics in the region of Saguenay-Lac-St-Jean, Quebec, Canada. Frequent use of healthcare services was defined as 4 visits or more to the Emergency Department (ED) and/or 3 hospitalizations or more in the previous year. Intervention: Case managers identified frequent users of each primary care clinic with the computerized platform of the healthcare centers. Primary care nurses worked in close collaboration with case managers to develop an individualized services plan and ensure coordination and self-management support during a period of 6 months. Methods: The mixed data collection included, at baseline and 6 months: 1) Semi-structured interviews with case managers, primary care nurses, programs managers, and patients, and 2 focus groups/clinic with family physicians and other professionals; 2) Participant observation of 7 meetings among the research team and managers responsible of the implementation, and non-participant observation of case management activities (25 hours); 3) Self-administered questionnaires (age, sex, marital status, education, occupation, family income and perception of the economic situation, health literacy, multimorbidity, integration of services, self-management of health and quality of life) completed by frequent users who received case management; 4) Services use (ED visits, hospitalizations and primary care visit) measured in the electronic medical record; 5) Intervention fidelity. Anticipated results: Multiple case study results will be presented during the NAPCRG 2020 conference annual meeting. Conclusion: This study will provide an in-depth portrait on implementation of this intervention and its impacts for patients, and the healthcare system.