We undertook a prospective study of 377 children (two to 16 years old) presenting with abdominal pain to determine: 1) common discharge diagnoses; 2) what signs and symptoms are associated with appendicitis; and 3) follow-up of patients discharged from the emergency department (ED). Nine diagnoses accounted for 86% of all diagnoses made. The most common final diagnosis was "abdominal pain" (36%). The following findings were significantly associated with appendicitis: vomiting, right lower quadrant(RLQ) pain, tenderness, and guarding (all P less than 0.001). Ninety-seven percent (28/29) of patients with appendicitis had at least two of these four signs and symptoms, as did 28% (96/348) of patients without appendicitis. The sensitivity of the model is 0.96, and the specificity is 0.72 (positive predictive value = 0.24; negative predictive value = 0.99). Of the patients contacted within one week of the visit (237), 75% reported that the pain had resolved (mean contact time, 2.6 days). We conclude that 1) patients presenting to the ED with abdominal pain often leave with the diagnosis of abdominal pain; 2) of the patients contacted, the majority reported that their pain has resolved; and 3) a diagnosis of appendicitis should be considered in any patient with any two of the following signs or symptoms: vomiting, guarding, tenderness, or RLQ pain. Such patients should be evaluated and observed carefully for the possible diagnosis of appendicitis.