Study Objective: Imaging studies in emergency department (ED) evaluation of pediatric appendicitis are obtained not only for diagnosis but to identify perforation and avoid negative appendectomy (NA). While imaging rates increased over the last decade in adults and children, perforation rates decreased only among adults. We sought to describe trends in imaging and to identify predictors of NA and perforation in pediatric ED patients with acute appendicitis. Methods: This retrospective cohort study included ED patients aged 2-17 years who underwent non-incidental appendectomy in a 21-hospital health care system from 2010-2015. Patients with appendicitis, appendectomy, NA and perforation were identified using ICD-9 codes. We evaluated patient characteristics associated with imaging (ultrasound [US] or CT) for patients with a single study. Demographics, laboratory data and facility level variables were included. Proportions were compared using the chi-squared test; continuous values with the Wilcoxon-Mann-Whitney nonparametric test. To identify predictors of NA and perforation, we performed bivariate analysis of patient characteristics then constructed three agestratified multivariable models (age 2-5 yrs, 6-10 yrs, and 11-17 yrs) for each outcome. Results: Overall, 4320 patients met inclusion criteria. The proportion without imaging decreased from 29% in 2010 to 6% in 2015 and with multiple studies (CT and US) increased from 8% to 24%. The proportion with CT decreased from 47% to 30%, and US increased from 16% to 40%. Increased CT utilization was associated with ED arrival between 12am-8am, body weight >90th percentile, older age and higher white blood cell (WBC) count, while US was associated with clinic visit >72 hrs before ED visit and shorter ED length of stay (LOS), see Table. Facility capacity for pediatric surgery was not associated with imaging choice. The NA rate ranged from 4.5% to 7.8%, while perforation rate ranged from 16%-18% over the study period. Race did not alter odds of perforation or NA. In the three multivariable regression models, NA odds decreased for WBC count> 10,000, referent WBC count 10,000 (2-5 yrs adjusted odds ratio [AOR] 0.2, 95% CI 0.1-0.6; 6-10 yrs AOR 0.4, 95% CI 0.2-0.9; and 11-17 yrs AOR 0.3, 95% CI 0.2-0.5), while odds of perforation increased for WBC count> 10,000 only in 6-10 yrs (AOR 1.9, 95% CI 1.0-3.4) and 11-17 yrs (AOR 4.2, 95% CI 2.5-7.2). Conclusion: Fewer pediatric patients underwent appendectomy without imaging, but NA and perforation rates did not change over the study period. In a community ED setting, age, weight and ED arrival time were predictive of CT utilization for diagnosing appendicitis, although US was associated with shorter LOS. Elevated WBC count increased odds of perforation among older children, and decreased odds of NA among all age groups. Race did not alter odds of perforation, unlike other studies, perhaps due to differences in access, as all patients in our cohort were part of the healthcare system. Our results support the use of WBC count as a candidate predictor for outcomes in appendicitis, adding to its current use in appendicitis risk scores.