摘要Background There are different definitions to identify/classify children with medical complexity(CMC).We aimed to investigate and describe the definitions used to classify CMC in epidemiological studies.Methods PubMed,SciELO,LILACS,and EMBASE were searched from 2015 to 2020(last updated September 15th,2020)for original studies that presented the definition used to classify/identify CMC in the scientific research method.We applied the Preferred Reporting Items for Systematic Reviews and Meta-Analyses methodology.From the included studies,the following were identified:first author,year of publication,design,population,study period,the definition of CMC used,limitations,and strengths.Results Nine hundred and sixty-seven records were identified in the searched databases,and 42 met the inclusion criteria.Of the 42 studies included,the four most frequent definitions used in the articles included in this review were classification of CMC into nine diagnostic categories based on the International Classification of Diseases,Ninth Revision(ICD-9)(35.7％,15 articles);update of the previous classification for ICD-10 codes with the inclusion of other conditions in the definition(21.4％,nine articles);definition based on a medical complexity algorithm for classification(16.7％,seven articles);and a risk rating system(7.1％,three articles).Conclusions CMC definitions using diagnostic codes were more frequent.However,several limitations were found in its uses.Our research highlighted the need to improve health information systems to accurately characterize the CMC popula-tion and promote the provision of comprehensive care.