Background/PurposeTo identify factors associated with nonoperative treatment failure in pediatric perforated appendicitis compared to immediate appendectomy. MethodsAfter IRB approval, between September 2016 and August 2017, prospective data were recorded for children (age: 1–18 years) with completed appendectomies and pathologist-confirmed perforations. Children were treated according to clinician-designated preference. Nonoperative treatment was considered failed if a nonresolving obstruction developed or any return of symptoms before the planned interval. The median time from pain onset to treatment initiation was 3 days (range: 1–14). Presentation on days 1 or 2 (early) was compared to day 3 or after(late). The nonoperatives were compared to appendectomies stratified by presentation time. Variables were compared by chi-square, Fisher exact or t-tests. Logistic regression evaluated for independence. ResultsOf 201 suspected perforations, 176 were included, 101 (57%) immediate appendectomies and 75 (43%) nonoperatives. Of 75, 24 (32%) failed; 6 (25%) in hospital, 18 (75%) after discharge. In 51 (68%), nonoperative treatment succeeded. Significantly younger children failed nonoperative treatment (p = 0.03). Failure was independently associated with treatment initiation within 2.75 days from pain onset (OR: 0.07, 95% CI: 0.57–0.98) (p = 0.010) and lower WBC at presentation (OR: 0.03, 95% CI: 0.81–0.98) (p = 0.014). When compared to immediate appendectomy, nonoperatives had more morbidity. ConclusionYounger children fail nonoperative treatment, perforate rapidly and have a significantly lower WBC, but benefit from immediate appendectomy. Level of evidenceTreatment Study Level II.