PurposeMegaprojects are large-scale and long-term investments. Three pillars of sustainable construction objectives, namely, social, environmental and economic, should be integrated into megaproject risk management to ensure long-term success. A risk assessment method, Risk Assessment Method for Sustainable Construction Objectives in Megaprojects (RAMSCOM), was developed for this purpose.Design/methodology/approachRAMSCOM was developed based on the latest concepts and identifying relevant and critical sustainability objectives and risks through an extensive literature review. Analytical Hierarchy Process (AHP) and Cross-Impact Analysis (CIA) were used to determine and quantify the threats regarding the importance of the sustainability objectives. The applicability of RAMSCOM was demonstrated on a real megaproject.FindingsThe findings revealed that sustainability risk assessment requires integration of economic, environmental, social objectives and analysis of cross-impacts of risk factors. Visualization of interrelated threats, vulnerabilities and objectives has a potential to support risk mitigation decisions to achieve sustainability goals.Research limitations/implicationsThe method has been developed based on the findings from a detailed literature survey on sustainability objectives and risks. RAMSCOM was tested on a single project with the assistance of three experts' views. Findings from the case project cannot be directly generalised for various megaprojects considering the unique nature of megaprojects.Practical implicationsDecision-makers can use RAMSCOM to assess sustainability risks in megaprojects and develop risk management plans for the most vulnerable and important sustainable objectives in a visual and quantified approach to ensure megaproject's sustainability in the long-term.Originality/valueThe theoretical contribution is a novel risk assessment method that integrates all dimensions of sustainability and quantifies the vulnerability of sustainability objectives considering their priorities, interrelations and risks. Sustainability dimensions, objectives and risks used in RAMSCOM can be useful for other researchers aiming to develop similar methods.