Background: In the Netherlands, suicide rates showed a sharp incline and this pertains particularly to the province of Noord-Brabant, one of the southern provinces in the Netherlands. This calls for a regional suicide prevention effort. Methods/design: Study protocol. A regional suicide prevention systems intervention is implemented and evaluated by a stepped wedge trial design in five specialist mental health institutions and their adherent chain partners. Our system intervention is called SUPREMOCOL, which stands for Suicide Prevention by Monitoring and Collaborative Care, and focuses on four pillars: 1) recognition of people at risk for suicide by the development and implementation of a monitoring system with decision aid, 2) swift access to specialist care of people at risk, 3) positioning nurse care managers for collaborative care case management, and 4) 12 months telephone follow up. Eligible patients are persons attempting suicide or expressing suicidal ideation. Primary outcome is number of completed suicides, as reported by Statistics Netherlands and regional Public Health Institutes. Secondary outcome is number of attempted suicides, as reported by the regional ambulance transport and police. Suicidal ideation of persons registered in the monitoring system will, be assessed by the PHQ-9 and SIDAS questionnaires at baseline and 3, 6, 9 and 12 months after registration, and used as exploratory process measure. The impact of the intervention will be evaluated by means of the RE-AIM dimensions reach, efficacy, adoption, implementation, and maintenance. Intervention integrity will be assessed and taken into account in the analysis. Discussion: The present manuscript presents the design and development of the SUPREMOCOL study. The ultimate goal is to lower the completed suicides rate by 20%, compared to the control period and compared to other provinces in the Netherlands. Moreover, our goal is to provide specialist mental health institutions and chain partners with a sustainable and adoptable intervention ...