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49 Prevalence of functional defecation disorders 1 children with underlying pathology. One of the Rome criteria for FC is the detection of a large fecal mass in the rectum. Since most epidemiological studies assessing the prevalence of FC are cross-sectional survey studies without a physical examination, it could be that the actual prevalence of FC is higher than reported in these studies, because one of the Rome criteria was not assessed. Furthermore, since there is currently no gold-standard quality assessment tool for epidemiological studies, we performed a quality assessment using a self-developed instrument. In summary, this systematic review of the current literature shows that FDDs are common in children worldwide. Geographical location was associated with the prevalence of FC, with the highest prevalence reported in the Americas and Europe. No associations with age or sex distribution were observed for FC. Data on FNRFI were scarce and no significant associations were found. Future studies according to the new Rome IV criteria are needed. Furthermore, studies with a longitudinal design could provide more insight in the epidemiology and the potential role of associated factors of FC and FNRFI in the pathogenesis. ACKNOWLEDGEMENTS The authors would like to thank E.E.W. Kramer for her help during the data collection.