CONTEXT Multiple scores exist to characterize organ dysfunction in children. OBJECTIVE To review the literature on multiple organ dysfunction (MOD) scoring systems to estimate severity of illness and to characterize the performance characteristics of currently used scoring tools and clinical assessments for organ dysfunction in critically ill children. DATA SOURCES Electronic searches of PubMed and Embase were conducted from January 1992 to January 2020. STUDY SELECTION Studies were included if they evaluated critically ill children with MOD, evaluated the performance characteristics of scoring tools for MOD, and assessed outcomes related to mortality, functional status, organ-specific outcomes, or other patient-centered outcomes. DATA EXTRACTION Data were abstracted into a standard data extraction form by a task force member. RESULTS Of 1152 unique abstracts screened, 156 full text studies were assessed including a total of 54 eligible studies. The most commonly reported scores were the Pediatric Logistic Organ Dysfunction Score (PELOD), pediatric Sequential Organ Failure Assessment score (pSOFA), Pediatric Index of Mortality (PIM), PRISM, and counts of organ dysfunction using the International Pediatric Sepsis Definition Consensus Conference. Cut-offs for specific organ dysfunction criteria, diagnostic elements included, and use of counts versus weighting varied substantially. LIMITATIONS While scores demonstrated an increase in mortality associated with the severity and number of organ dysfunctions, the performance ranged widely. CONCLUSIONS The multitude of scores on organ dysfunction to assess severity of illness indicates a need for unified and data-driven organ dysfunction criteria, derived and validated in large, heterogenous international databases of critically ill children.