CONTEXT: Unplanned PICU readmissions within 48 hours of discharge (to home or a different hospital setting) are considered a quality metric of critical care. OBJECTIVE: We sought to determine identifiable risk factors associated with early unplanned PICU readmissions. DATA SOURCES: A comprehensive search of Medline, Embase, the Cochrane Database of Systematic Reviews, and Scopus was conducted from each database s inception to July 16, 2018. STUDY SELECTION: Observational studies of early unplanned PICU readmissions (,48 hours) in children (,18 years of age) published in any language were included. DATA EXTRACTION: Two reviewers selected and appraised studies independently and abstracted data. A meta-Analysis was performed by using the random-effects model. RESULTS: We included 11 observational studies in which 128 974 children (mean age: 5 years) were evaluated. The presence of complex chronic diseases (odds ratio 2.42; 95% confidence interval 1.06 to 5.55; I2 79.90%) and moderate to severe disability (odds ratio 2.85; 95% confidence interval 2.40 to 3.40; I2 11.20%) had the highest odds of early unplanned PICU readmission. Other significant risk factors included an unplanned index admission, initial admission to a general medical ward, spring season, respiratory diagnoses, and longer initial PICU stay. Readmission was less likely after trauma-and surgery-related index admissions, after direct admission from home, or during the summer season. Modifiable risk factors, such as evening or weekend discharge, revealed no statistically significant association. Included studies were retrospective, which limited our ability to account for all potential confounders and establish causality. CONCLUSIONS: Many risk factors for early unplanned PICU readmission are not modifiable, which brings into question the usefulness of this quality measure.