Of 212 cases of peritonitis found in a retrospective study of geriatic inpatients, the most common causes were mesenteric infarction, malignancy, intestinal obstruction, perforated peptic ulcer, cholecystitis, diverticulitis and perforation of the urinary bladder. The diagnostic accuracy was 47%. Abdominal pain had been observed in only 55% of the cases, and guarding and/or abdominal rigidity in only 34%. Other findings such as tachycardia and fever were more common, but the specificities of these signs were low.