Diarrhea is one of the most important diseases in young foals and may occur in more than half of foals until weaning age. Several infectious and noninfectious underlying causes have been implicated but scientific evidence of pathogenesis is evolving. It is important to investigate all known potential causes and identify infectious agents to avoid outbreaks, evaluate the level of systemic compromise, and establish adequate therapy. It is crucial to differentiate foals that can be managed in field conditions from those that should be sent to a referral center. This article reviews these aspects and recent developments in the diagnostic and therapeutic approaches.