Acute gastroenteritis accounts for millions of deaths each year in young children, mostly in developing communities. In developed countries it is a common reason for presentation to general practice or emergency departments and for admission to hospital. Dehydration, which may be associated with electrolyte disturbance and metabolic acidosis, is the most frequent and dangerous complication. Optimal management with oral or intravenous fluids minimises the risk of dehydration and its adverse outcomes. Routine use of antibiotics, antidiarrhoeal agents, and antiemetics is not recommended and may cause harm. Prevention is the key to controlling gastroenteritis, and recently licensed, highly effective rotavirus vaccines will have a major effect on public health.