The increased frequency and magnitude of natural disasters is producing a growing awareness of the need to incorporate mental well-being and resilience into policy and practice. The present research uses mental well-being impact assessment (MWIA) to identify and describe the main factors enhancing mental well-being of people affected by a tsunami on Robinson Crusoe Island in 2010, and explores their effects on people's resilience. The main factors were: the natural environment, meaningful activities, local food, social activities, lifelong learning, transport and security. These factors influenced mental well-being through four main environmental dimensions: ecology, culture, milieu and organization. They could influence mental well-being in a constant, multiple and cumulative way. The findings of this research provide a significant practical knowledge for the improvement of MWIA practice.