This study has looked at the costs and benefits of a proposed flood adaptation project in one of the country’s most flood-prone areas, the Xuan Tributary in Thua Thien-Hue province. Results indicate that upgrading the flood defenses and drainage systems along the entire An Xuan tributary would bring a wide range of economic and social benefits at both the household and community level. It also found that the value of these benefits would far outweigh any costs. It therefore recommends that the government should invest in the project.