Research was conducted in rural Northeast Thailand to understand how mothers perceive children's acute illness episodes, and their resulting illness management strategies. Although diarrheal disease is one of the leading causes of illness among young children in Thailand, interviews revealed that mothers frequently do not classify infantile diarrhea as an “illness.” Infantile diarrhea is commonly labeled thai su, a type of diarrhea believed necessary to “lighten the body” so that the infant can attain a new developmental stage, such as sitting up, standing, or walking. Consequently, mothers do not perceive infection-related diarrheal illness as common in infants, and therefore do not direct much attention to prevention, nor manage diarrheal cases in a manner consistent with biomedical recommendations. In this article I describe local explanatory models of diarrheal illness, and discuss the role of situational factors and elder authority in determining how illness episodes are assessed and managed.