The study of acute appendicitis, unperforated and perforated, has been conducted by a group of us1since the autumn of 1939 by means of a survey of cases in metropolitan Cleveland from Jan. 1, 1930 to Jan. 1, 1942. In those twelve years there occurred 19,401 instances of the affliction in this area, which corresponds to all Cuyahoga County, in which Cleveland is located. The case records are drawn from the sixteen largest hospitals in the county, and these represent the great majority of all hospital beds in the community. Diagnosis of the condition in each case is based on the pathologist's report. We did not attempt to analyze any records in which chronic appendicitis or anything similar appeared because of disagreements of criteria. Therefore in this report the cases are grouped under one of three headings: (1) acute simple appendicitis, unperforated, (2) perforative appendicitis with peritonitis and (3)