Importance: The influence of disease severity on outcomes and use of health care resources in children with complicated appendicitis is poorly characterized. Adjustment for variation in disease severity may have implications for ensuring fair reimbursement and comparative performance reporting among hospitals. Objective: To examine the association of intraoperative findings as a measure of disease severity with complication rates and resource use in children with complicated appendicitis. Design: This retrospective cohort study used clinical data from the American College of Surgeons National Surgical Quality Improvement Program pediatric appendectomy pilot database (NSQIP-P database) and cost data from the Pediatric Health Information System database. Twenty-two children's hospitals participated in the NSQIP Pediatric Appendectomy Collaborative Pilot Project. Patients aged 3 to 18 years with complicated appendicitis who underwent an appendectomy from January 1, 2013, through December 31, 2014, were included in the study. Appendicitis was categorized in the NSQIP-P database as complicated if any of the following 4 intraoperative findings occurred in the operative report: visible hole, fibropurulent exudate in more than 2 quadrants, abscess, or extraluminal fecalith. Data were analyzed from January 1, 2013, through December 31, 2014. Main Outcomes and Measures: Thirty-day postoperative adverse event rate, revisit rate, hospital cost, and length of stay. Multivariable regression was used to estimate event rates and outcomes for all observed combinations of intraoperative findings, with adjusting for patient characteristics and clustering within hospitals. Results: A total of 1333 patients (58.7% boys; median age, 10 years; interquartile range, 7-12 years) were included; multiple intraoperative findings of complicated appendicitis were reported in 589 (44.2%). Compared with single findings, the presence of multiple findings was associated with higher rates of surgical site infection (odds ratio, 1.40; 95% CI, 0.95-2.06; P =.09), higher revisit rates (odds ratio, 1.60; 95% CI, 1.15-2.21; P =.005), longer length of stay (rate ratio, 1.45; 95% CI, 1.36-1.55; P <.001), and higher hospital cost (rate ratio, 1.35; 95% CI, 1.19-1.53; P <.001). Significant differences were found among different combinations of intraoperative findings for all outcomes, including a 3.6-fold difference in rates of surgical site infection (range, 7.5% for fecalith alone to 27.2% for all 4 findings; P =.002), a 2.6-fold difference in revisit rates (range, 8.9% for exudate alone to 22.9% for all 4 findings; P =.001), a 2.2-fold difference in length of stay (range, 4.0 days for exudate alone to 8.9 days for all 4 findings; P <.001), and a 2.4-fold difference in mean cumulative cost (range, $13296 for exudate alone to $32282 for all 4 findings; P <.001). Conclusions and Relevance: More severe presentations of complicated appendicitis are associated with worse outcomes and greater resource use. Severity adjustment may be needed to ensure fair reimbursement and comparative performance reporting, particularly at hospitals treating underserved populations where more severe presentations are common.