Appendicitis was rare in the past and still is in traditional Third World populations. It began to increase a century ago, peaked about 1950, and has now fallen to about half its previous incidence. As to causation, dietetically, it was contended that the increase was promoted primarily by an associated fall in dietary fiber intake. The recently advanced hygiene hypothesis considers the increase to have stemmed from improvements in hygiene, generally; these limited exposure to enteric infections and modified response to virus infections, thereby triggering appendicitis. Major uncertainties still prevail over the promotive and precipitating factors of the disease. It is doubtful whether individuals can take any action to avoid appendicitis.