Diabetes mellitus is one of the most frequent systemic disorders in medically compromised dental patients. Since it seems to be a significant relationship between diabetes mellitus and apical pathology, any diabetic dental patients should be suspected to develop chronic apical periodontitis both in endodontically treated and untreated teeth. A proper follow-up of root-filled teeth associated with periodical glycaemia control is mandatory to increase their survival. The diabetic status of a patient should be a key prognostic factor of decision in conservative endodontic managemen