Appendicitis is the inflammation of a person's appendix. The appendix is a pouch at the start of the large intestine. Symptoms usually include a sharp abdominal pain in the lower right part. Also, nausea, vomiting, and decreased appetite are common.^[1] However, about 40% of people do not have these typical symptoms.^[1] If the appendix ruptures (splits) the result is painful peritonitis,^[2] and possible sepsis. Immediate treatment in hospital is needed for appendicitis. Usually the infected appendix is taken out.^[source?]

Some people think the function of the appendix in apes is the digestion of vegetation (vegetable) matter such as leaves. Humans do not digest leaves, but they inherited some of the apes' vegetarian apparatus. The human appendix is much smaller than that of present-day apes, and for some reason, the immune system can try to fight it. An appendix infection not eliminated as it might be somewhere else in the body.

The causes of appendicitis include blocking in the appendix, or bacterial infections.^[3] If it is not treated, it may lead to peritonitis and shock. Most serious appendicitis happens to younger children and elder adults. Appendicitis is common between the ages of ten and fourteen for males, and fifteen and nineteen for females.^[4] The most usual treatment is an appendectomy, which means removing the appendix. Sometimes it gets better without surgery. Some people think that eating vegetables will help^[4][5] but this is not an alternative to treatment.

Reginald Fitz first described acute appendicitis in 1886.^[6]

It is one of the leading causes worldwide of "pain in the abdomen", a term used in medicine and surgery to cover a wide range of causes.

• Pancreatitis
• Gallstones