Acute abdominal pain is a common complaint among paediatric patients visiting the emergency department (ED). Functional abdominal pain is not associated with any surgical or infectious etiology and is a frequent cause of painful abdominal cramps. Although functional abdominal pain is not life-threatening, it has significant impact on quality of life, functional outcomes, and patient satisfaction. It is a major source of school and work absence, loss of sleep, and extracurricular impairment. Despite this, analgesia has traditionally been withheld from patients with acute abdominal pain. The reasons behind this are likely two-fold. First, there is good evidence that clinicians fear that analgesia will mask signs of an underlying surgical pathology such as appendicitis. There is no current published literature that supports this practice. In fact, recent evidence has found that providing analgesia to children does not obscure signs of an acute surgical abdomen nor lead to clinically significant differences in negative outcomes. Second, there is no standard of care specifying the best analgesic options for treating abdominal pain in children in the post-codeine era. Although acetaminophen, ibuprofen, ketorolac, buscopan, and almagel/viscous lidocaine are frequently used agents in the ED, evidence for their benefit in children with functional abdominal pain is lacking. As a predictable result, most patients who present with abdominal pain fail to experience pain relief at discharge. The importance of providing optimal pain treatment is echoed by several national and international level policy statements. In addition to the World Health Organization (WHO)'s mandate that adequate pain treatment should be a fundamental human right, the American Academy of Pediatrics (AAP) has reaffirmed its position that adequate analgesia be provided for children. Furthermore, literature supports that providing analgesia improves patient care, caregiver satisfaction, and the therapeutic relationship. Antispasmodics are commonly used agents to treat abdominal cramping. Hyoscine butylbromide (HBB), trade name: Buscopan, is an anticholinergic agent that when orally administered, does not cross the blood brain barrier and has minimal systemic absorption. Therefore, it inhibits bowel motility without central nervous system or peripheral side effects. This antispasmodic has been used in clinical practice for over 60 years and specifically has been on the market since 1952 for the treatment of abdominal cramps. It is widely available around the world as both a prescription drug and an over the counter medication in many industrialized countries. It has also been used safely in neonates and children. As hyoscine butylbromide is barely absorbed, it is generally well tolerated. In the two large-scale studies of almost 1200 patients that compared HBB with placebo (and paracetamol), there was no significant difference in adverse events between the two groups, including those commonly associated with anticholinergics, such as nausea, constipation, dry mouth, blurred vision, tachycardia and urinary retention. Moreover, these adverse events not only occurred at a low incidence (less than or equal to 1.5%) but were also usually mild and self-limiting. In abdominal cramping and pain associated with irritable bowel syndrome, systematic reviews have had conflicting results with regards to analgesic efficacy, primarily because of small sample sizes and less rigorous designs. Muller-Krampe et al. conducted a prospective cohort of over 200 children with both acute and chronic abdominal spasms and compared the effectiveness of oral HBB 10 mg to a homeopathic preparation. HBB demonstrated comparative improvements to the homeopathic preparation with respect to pain, sleep disturbance, eating and drinking, and crying. Over 90% of patients in both groups reported good tolerability and there were no adverse events. Although HBB is used widely for abdominal pain in children and anecdotal evidence suggests it is efficacious, no paediatric clinical trial to date has explored its efficacy in the ED setting. The investigators hypothesize that HBB will have superior efficacy to the most commonly used agent, acetaminophen for acute abdominal pain in children. If HBB is found to be an effective analgesic in children with acute abdominal pain, it could provide a therapeutic option for a common, painful condition for which there is currently very little to offer.