OBJECTIVE: To compare rates of postoperative drainage and culture profiles in children with complicated appendicitis treated with the two most common antibiotic regimens with and without antipseudomonal activity (piperacillin-tazobactam [PT] and ceftriaxone with metronidazole [CM]). SUMMARY OF BACKGROUND DATA: Variation in use of antipseudomonal antibiotics has been driven by a paucity of multicenter data reporting clinically relevant, culture-based outcomes. METHODS: Retrospective cohort study of patients with complicated appendicitis (7/2015-6/2020) using NSQIP-Pediatric data from 15 hospitals participating in a regional research consortium. Operative report details, antibiotic utilization, and culture data were obtained through supplemental chart review. Rates of 30-day postoperative drainage and organism-specific culture positivity were compared between groups using mixed effects regression to adjust for clustering after propensity matching on measures of disease severity. RESULTS: 1002 children met criteria for matching (58.9% received CM and 41.1% received PT). In the matched sample of 778 patients, children treated with PT had similar rates of drainage overall (PT: 11.8%, CM: 12.1%; OR 1.44 [OR:0.71-2.94]) and higher rates of drainage associated with growth of any organism (PT: 7.7%, CM: 4.6%; OR 2.41 [95%CI:1.08-5.39]) and Escherichia coli (PT: 4.6%, CM: 1.8%; OR 3.42 [95%CI:1.07-10.92]) compared to treatment with CM. Rates were similar between groups for drainage associated with multiple organisms (PT: 2.6%, CM: 1.5%; OR 3.81 [95%CI:0.96-15.08]) and Pseudomonas (PT: 1.0%, CM: 1.3%; OR 3.42 [95%CI:0.55-21.28]). CONCLUSIONS AND RELEVANCE: Use of antipseudomonal antibiotics is not associated with lower rates of postoperative drainage procedures or more favorable culture profiles in children with complicated appendicitis.