The treatment of appendiceal abscess is controversial. For patients initially treated "conservatively" with antibiotics with or without drainage, the role of interval appendectomy is an area of considerable debate. Without interval appendectomy, the true risks of recurrent disease and missed pathological findings are uncertain, and large, long-term, prospective studies are unavailable. To evaluate the role of interval appendectomy, the authors reviewed the histopathologic specimens from patients with presumed appendiceal abscess treated by interval appendectomy. Over a 7-year period, 162 children presented with a clinical diagnosis of perforated appendicitis. Eighteen patients had localized abscesses treated conservatively, followed by interval appendectomy. Standard histopathologic sections of 17 of the 18 appendices were examined by one pathologist who was blinded to the clinical data and to the interpretation of the original pathologist. Of the 11 boys and seven girls (mean age, 7.4 +/- 3.4 years), eight underwent percutaneous drainage and one underwent operative drainage. All received intravenous antibiotics for a mean of 8.6 +/- 3.2 days with a hospital stay of 10.4 +/- 8.3 days. Interval appendectomy was performed at a mean of 92.7 +/- 20.7 days after initial admission, with discharge at a mean of 2 +/- 1.3 days after surgery. There were no complications or deaths. Histopathologic review showed normal appendix (n = 4), normal appendix with mild serositis (n = 6), normal appendix with unsuspected resolved Meckel's diverticulitis (n = 1), appendiceal duplication (n = 1), granulomatous appendicitis (n = 3), and acute appendicitis (n = 2). All appendices had patent lumens, and 15 were documented to be present to the tip. There was no correlation between the histopathologic findings and the interval between abscess and interval appendectomy. Interval appendectomy was performed with no morbidity and a short hospital stay. Two patients had histopathologic recurrent acute appendicitis, five had unsuspected pathological findings (appendiceal duplication, Meckel's diverticulitis, granulomatous inflammation), and none of the appendices had an obliterated lumen, suggesting that all patients were at long-term risk for recurrent disease. These data support the role of interval appendectomy in cases of perforated appendicitis treated conservatively.