Objective This study aims to investigate the diagnosis and treatment of external root resorption of adjacent teeth caused by impacted teeth via cone-beam computed tomography (CBCT).Methods A total of 19 teeth from 15 patients with uncertain external root resorption caused by an adjacent impacted tooth were examined from January 2011 to December 2011. All teeth with uncertain external root resorption were scanned by CBCT. Three dimensions reconstruction were the con-ducted to determine the location and extent of resorption.Results In all cases, CBCT identified the accurate location and extent of external root resorption caused by adjacent impacted teeth. Furthermore, the technique provided impacted teeth location in three dimensions, including the relation between the impacted teeth and surrounding vital structures.Conclusion CBCT can provide direct and accurate images of the location and extent of external root resorption, as well as the location of the adja-cent impacted teeth in three dimensions. Therefore, the proposed technique provides reliable information for clinical diagnosis and treatment.