Acute appendicitis is the most common abdominal surgical emergency in children, and appendectomy is the most frequent acute abdominal operation. Prompt diagnosis and surgical treatment are required to reduce the risk of perforation and prevent complications, especially in small children. Enterochromaffin cells that contain large amounts of serotonin are mostly located in the distal appendix. Serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) could therefore be a marker for acute appendicitis.