BACKGROUND AND OBJECTIVES: Appendicitis guidelines recommend either narrower- or extended- spectrum antibiotics for treatment of complicated appendicitis. The goal of this study was to compare the effectiveness of extended-spectrum versus narrower-spectrum antibiotics for children with appendicitis. METHODS: We performed a retrospective cohort study of children aged 3 to 18 years discharged between 2011 and 2013 from 23 freestanding children's hospitals with an appendicitis diagnosis and appendectomy performed. Subjects were classified as having complicated appendicitis if they had a postoperative length of stay ≥3 days, a central venous catheter placed, major or severe illness classification, or ICU admission. The exposure of interest was receipt of systemic extended-spectrum antibiotics (piperacillin ± tazobactam, ticarcillin ± clavulanate, ceftazidime, cefepime, or a carbapenem) on the day of appendectomy or the day after. The primary outcome was 30-day readmission for wound infection or repeat abdominal surgery. Multivariable logistic regression, propensity score weighting, and subgroup analyses were used to control for confounding by indication. RESULTS: Of 24 984 patients, 17 654 (70.7%) had uncomplicated appendicitis and 7330 (29.3%) had complicated appendicitis. Overall, 664 (2.7%) patients experienced the primary outcome, 1.1% among uncomplicated cases and 6.4% among complicated cases (P < .001). Extended-spectrum antibiotic exposure was significantly associated with the primary outcome in complicated (adjusted odds ratio, 1.43 [95% confidence interval, 1.06 to 1.93]), but not uncomplicated, (adjusted odds ratio, 1.32 [95% confidence interval, 0.88 to 1.98]) appendicitis. These odds ratios remained consistent across additional analyses. CONCLUSIONS: Extended-spectrum antibiotics seem to offer no advantage over narrower-spectrum agents for children with surgically managed acute uncomplicated or complicated appendicitis.