Localized air-fluid levels, localized ileus, or increased soft tissue density in the right lower quadrant is present in 50% of patients with early acute appendicitis. Less common findings are a calculus, an altered right psoas shadow, or an abnormal right flank stripe. The finding on plain films of a calculus in the right lower quadrant coupled with pain in this area strongly supports a diagnosis of appendicitis. Although perforated peptic ulcer is by far the most common cause of free intraperitoneal air, free air is also a rare manifestation of perforated appendicitis. In general, however, the findings on plain films are nonspecific and rarely of help in diagnosis. A suggestion that barium enema may contribute to the diagnosis has not been supported by experience.