OBJECTIVE:To investigate evolving food retail systems in Thailand. DESIGN:Rapid assessment procedures based on qualitative research methods including interviews, focus groups discussions and site visits. SETTING:Seven fresh markets located in the four main regions of Thailand. SUBJECTS:Managers, food specialists, vendors and shoppers from seven fresh markets who participated in interviews and focus group discussions. RESULTS:Fresh markets are under economic pressure and are declining in number. They are attempting to resist the competition from supermarkets by improving convenience, food diversity, quality and safety. CONCLUSIONS:Obesity has increased in Thailand at the same time as rapid growth of modern food retail formats has occurred. As fresh markets are overtaken by supermarkets there is a likely loss of fresh, healthy, affordable food for poorer Thais, and a diminution of regional culinary culture, women's jobs and social capital, with implications for the health and nutrition transition in Thailand.