The mortality rate for appendicitis in children has remained relatively unchanged since the 1940s, when antibiotics were introduced in the treatment of appendiceal peritonitis. However, since this time the incidence of appendiceal rupture has increased appreciably, presumably owing to a failure of early recognition and treatment. At Columbus Children's Hospital, one half of all patients undergoing appendectomy for ruptured appendix in 1975 had been seen by another physician before admission, but the correct diagnosis had not been made. The history obtained by the primary physician and that given on admission were similar, yet differed from the histories given by patients whose disease had been correctly diagnosed. Findings on in-hospital physical examination of incorrectly diagnosed patients differed from those recorded by the primary physician, but were similar to those of patients whose disease had been correctly diagnosed. Since it is unlikely that the natural history of the disease has changed, the increased incidence of rupture must result either from early misinterpretation of physical findings or from greater delay by parents in responding to the child's illness. Physicians and parents must share the responsibility equally for the increasing incidence of appendiceal rupture in children.