This systematic review analysed the literature comparing marginal adaptation of mineral trioxide aggregate (MTA) with other filling materials in root-end cavities. The PubMed, Ovid, Web of Science, SCOPUS, and Cochrane library databases were searched using appropriate keywords related to root-end filling materials and adaptation. Of 38 articles assessed, 20 met the inclusion criteria. No in vivo study was identified. In 10 studies, MTA gave the best marginal adaptation results, but no significant differences were found between MTA and any of the tested filling materials in seven studies. There was great variability in the study designs including analysed surface, unit of gap measurement and magnification amount during analysis. On the basis of available evidence, MTA presented good marginal adaptation to dentine walls. This review identified the need for the development of standardised methods to evaluate the adaptation property of root-end filling materials in ex vivo studies as well as in clinical studies evaluating outcome.