Acute pancreatitis affects 300 to 600 new patients per million population per year and is most commonly caused by gallstones or alcohol, but there are many other causes and associations. Careful imaging reveals that most so-called idiopathic acute pancreatitis is due to small (1–3 mm diameter) gallstones. Diagnosis is made by a combination of a typical presentation (upper abdominal pain and vomiting) in conjunction with raised serum amylase (> × 3 upper limit of normal) and/or lipase (> × 2 upper limit of normal). Several acute abdominal emergencies can mimic acute pancreatitis and may be associated with a raised serum amylase. These include perforated peptic ulcer (particularly perforated posterior gastric ulcer) and acute mesenteric ischaemia. In equivocal cases, a CT scan is indicated in order to exclude other causes and confirm the diagnosis....