This study examines the major health, water, environmental, tourism and other welfare impacts associated with poor sanitation in Cambodia, Indonesia, the Philippines and Vietnam. The study is based on evidence from other investigations, surveys and databases. The impact measurement reported in the study focuses mainly on a narrow definition of sanitation − human excreta management and related hygiene practices. The measurement of water resource impact also includes grey water, and the measurement of environmental impact includes solid waste management. By examining the economic impacts of poor sanitation, and the potential gains from improved sanitation, this study provides important evidence to support further investment in sanitation. The goal of this report is to show decision-makers at the country and regional levels how the negative impacts of poor sanitation can be mitigated by investing in improved sanitation.