Acute gastrointestinal disorders are among the most common problems encountered by the emergency physician. Serum electrolytes are commonly ordered in the evaluation of patients with gastroenteritis. We retrospectively reviewed the charts of all 281 patients with a discharge diagnosis of acute gastroenteritis seen in our emergency department during a recent six-month period. Electrolytes were ordered on 207 of these patients, and the time spent in the ED was three to four times longer for patients on whom electrolytes were ordered. Of these 207, 24 (11%) had electrolyte abnormalities, but only two (1%) had clinically significant electrolyte abnormalities, which were defined as values that affected patient treatment or disposition. On presentation, 56 patients (27%) had orthostatic vital sign changes (defined as a pulse increase of 30 or more on standing). Five (10%) had electrolyte abnormalities. None of the abnormalities were clinically significant. Eleven patients (5%) were hospitalized. One patient had electrolyte abnormalities that were not the cause of hospitalization. No patients with uncomplicated gastroenteritis alone had clinically significant electrolyte abnormalities. We conclude that there is no justification for the routine ordering of serum electrolytes on the adult patient with acute gastroenteritis.