On he radiographic findings of simple abdomen, detection of free air in peritoneal cavity indicates aperforation of hollow viscus. In general, free air in abdomen indicate perforation of hollow viscus caused byvarious disease conditions, i.e. perforation of peptic ulcer, ulcerating malignancy, colon diverticulitis and rupture of pneumatosis cystoides intestinal etc., or by trauma, however it can be rarely noticeable in the cases of intraabdominal infection with over growth of gas forming organisms. Eighty-eight cases of free air in peritoneal cavity were analised during the period from July, 1970 to August, 1972 at Kyungpook National University Hospital. As shown in the following tables, various clinical findings were analised; overview of cases, causating factors and location of rupture, and it's seasonal preponderance.