Acute gastroenteritis remains a common illness among infants and children throughout the world. Among children in the United States, acute diarrhea accounts for >1.5 million outpatient visits, 200,000 hospitalizations, and approximately 300 deaths/year. In developing countries, diarrhea is a common cause of mortality among children aged <5 years, with an estimated 2 million deaths annually. Oral rehydration therapy (ORT) includes rehydration and maintenance fluids with oral rehydration solutions (ORS), combined with continued age-appropriate nutrition. Although ORT has been instrumental in improving health outcomes among children in developing countries, its use has lagged behind in the United States. This report provides a review of the historical background and physiologic basis for using ORT and provides recommendations for assessing and managing children with acute diarrhea, including those who have become dehydrated. Recent developments in the science of gastroenteritis management have substantially altered case management. Physicians now recognize that zinc supplementation can reduce the incidence and severity of diarrheal disease, and an ORS of reduced osmolarity (i.e., proportionally reduced concentrations of sodium and glucose) has been developed for global use. The combination of oral rehydration and early nutritional support has proven effective throughout the world in treating acute diarrhea. In 1992, CDC prepared the first national guidelines for managing childhood diarrhea (CDC. The management of acute diarrhea in children: oral rehydration, maintenance, and nutritional therapy. MMWR 1992;41[No. RR-16]), and this report updates those recommendations. This report reviews the historical background and scientific basis of ORT and provides a framework for assessing and treating infants and children who have acute diarrhea. The discussion focuses on common clinical scenarios and traditional practices, especially regarding continued feeding. Limitations of ORT, ongoing research in the areas of micronutrient supplements, and functional foods are reviewed as well. These updated recommendations were developed by specialists in managing gastroenteritis, in consultation with CDC and external consultants. Relevant literature was identified through an extensive MEDLINE search by using related terms. Articles were then reviewed for their relevance to pediatric practice, with emphasis on U.S. populations. Unpublished references were sought from the external consultants and other researchers. In the United States, adoption of these updated recommendations could substantially reduce medical costs and childhood hospitalizations and deaths caused by diarrhea.