This is a prospective, randomized double-blind, placebo-controlled clinical that will be conducted in the ED at Children's Medical Center of Dallas. Children aged 1 to 18 years with acute abdominal pain of ≤ 3 days duration, a moderate to severe pain score, and the presence of peritoneal signs will be eligible. Patients will be randomized to receive either 0.1mg/kg of intravenous morphine (maximum 10 mg) or an equal volume of placebo (0.9% saline).