One of the hollow organs of the abdomen or a major blood vessel may perforate spontaneously in the case of an ulcer or an advanced tumour or it may be secondary to trauma such as a knife wound or other penetrating injury from a traffic or industrial accident. Whatever the cause, perforation is a surgical emergency. The intestinal contents, which contain large numbers of bacteria, pass freely out into the abdominal cavity and cause a severe chemical or bacterial PERITONITIS. This is usually accompanied by severe abdominal pain, collapse or even death. There may also be evidence of free fluid or gas within the abdominal cavity. Surgical intervention, to repair the leak and wash out the contamination, is often necessary. Perforation or rupture of major blood vessels, whether from disease or injury, is an acute emergency for which urgent surgical repair is usually necessary. Perforation of hollow structures elsewhere than in the abdomen – for example, the heart or oesophagus – may be caused by congenital weaknesses, disease or injury. Treatment is usually surgical but depends on the cause.