In caring for patients with acute gastroenteritis, the physician's primary task is to assess the severity of illness and to tailor fluid and electrolyte replacement and symptomatic therapy accordingly. Antibiotics are seldom indicated for acute gastroenteritis, and it is up to the physician to make a rational, informed choice about their use. Narrowing the considerations in differential diagnosis can help guide decision making about the need for diagnostic tests, specific therapy, and public health intervention.