Periappendicitis has heretofore been regarded as a pathologic curiosity with little clinical significance. In this report, we have reviewed the UCLA experience with periappendicitis. Between 1955 and 1985, resected appendices of 353 patients showed periappendicitis on pathologic examination. Sixty-one of these patients, in whom exploratory surgery was performed for reasons other than acute appendicitis, underwent incidental appendectomy. In 251 of the remaining 292 patients, appendectomy was performed either for pathologically confirmed acute appendicitis or concomitant with treatment of other unsuspected abnormalities discovered intraoperatively. Although the remaining 41 patients were also believed to have acute appendicitis, their resected specimens revealed only periappendicitis. The latter group was composed of 9 males and 32 females, with a mean age of 29 years (range: 6 to 76 years). Twenty-four complications occurred in 18 of these patients (44%). Seven additional operative procedures were required in 5 of the 41 patients (12%). One patient died (2%). We conclude that identification of periappendicitis in the patient presumed to have acute appendicitis is of definite clinical significance and may merit further clinical investigation.