Background: Appendiceal mass and abscess and its treatment are associated with significant morbidity and high costs. Still, the optimal treatment strategy is the point of debate. Therefore, this systematic review and meta-analysis aimed to compare overall complications between initial non-operative treatment (NOT) and early appendectomy (EA) in children with appendiceal mass and/or abscess. Methods: Pubmed and Embase were searched. Only randomized controlled trials and prospective or historical cohort studies that compared NOT with EA in children with appendiceal mass or abscess in terms of complications were eligible for inclusion. Risk of bias was assessed. Primary outcome was the overall complication rate. Secondary, length of stay and readmission rate were investigated. A meta-analysis of overall complications associated with both treatment strategies was performed. Results: 14 of 7083 screened studies were selected, including 1022 children in the NOT group and 333 in the EA group. Duration of follow-up ranged between four weeks and 12 years. Risk of bias was moderate in four and serious in 10 studies. NOT was associated with a lower overall complication rate (risk ratio (RR) 0.37 [95% confidence interval (CI) 0.21–0.65]). However, NOT led to increased length of stay (mean difference varied between 0.2 and 8.4 days) and higher readmission rate (RR 1.75 [95%CI 0.79–3.89]), although not significantly. Interval appendectomy after NOT was performed as a routine procedure in all but one study. This study found a recurrence rate of 34% in a group of 38 patients during a follow-up period of 3.4 ± 1.7 years. Conclusion: NOT may reduce the overall complication rate compared to EA, but the evidence is very uncertain. As evidence is scarce, and of low level, and heterogeneity between studies is substantial, the results should be interpreted with caution. Large prospective studies are needed to determine the optimal treatment strategy for children with appendiceal mass and/or abscess.