The aim was to determine the impact of a case management model on indicators of health service utilization, polypharmacy, quality of life and dependency of patients with multimorbidity, and family caregiver overload in a group of patients insured with two insurance companies in the city of Bogotá (Colombia). This was a mixed methods study, which integrated a quantitative and qualitative component. The study was conducted between July 2019 and March 2020. A quantitative component is based on a pre-experimental study with a single group and pre- and post-test measurements. Patients with multimorbidity with a medium or high level of complexity were included in the study. A sample of 317 patients and their caregivers was estimated. Following the completion of the intervention, a descriptive study that explored the perspective of nurses, patients and caregivers was developed to better understand the process and results from their own words and experience. A total of 17 dyads of patients and caregivers were interviewed, as well as six nurse managers. The integration strategy was developed based on a comparison made from the perspective of multiple stakeholders. The model's impact on quality of life, particularly in terms of social functioning and mental health, has been documented. Caregiver overload was reduced and an improvement in the adoption of the role was observed, aspects that converge with the experience of the dyads and the caregivers in the support and backing provided by the model. The intervention was structured in five modules: case detection, complexity screening, comprehensive assessment with various instruments, individualized care and follow-up plan, and plan assessment. The nurse manager role is confirmed as that of a professional with the leadership capacity to articulate disciplines and actors, whilst also dealing with the day-to-day needs of people with complex health conditions. A comprehensive and integrated approach to patients with multiple diseases in a health insurance context marked by access barriers and fragmentation of health services. The study provides quantitative and qualitative evidence of the benefits of the case management model in Colombia for patients with multiple diseases and their family caregivers, particularly in terms of the psychosocial dimensions of health-related quality of life and dependence assessment. A significant impact on the caregiver role, as well as an improvement in perception and trust in the health system, was observed as a result of the overcoming of administrative barriers achieved by the nurse case manager. The findings are considered to be extremely useful for decision-makers and insurers in developing a case management model focused on comprehensive and individualized care plans, as well as for individuals with multiple diseases and their caregivers.