Internal inflammatory root resorption is a relatively rare resorption that begins in the root canal and destroys surrounding dental hard tissues. Odontoclastic multinuclear cells are responsible for the resorption, which can grow to perforate the root if untreated. The initiating factor in internal root resorption is thought to be trauma or chronic pulpal inflammation, but other etiological factors have also been suggested. Active, expanding resorption requires vital pulp tissue and continuous microbiological irritation, likely from the necrotic coronal part of the root canal. In its classical form, internal root resorption is easy to diagnose. However, in many instances advanced diagnostic methods may be required for a definitive diagnosis. Internal root resorption is usually symptom free, but in cases of perforation, a sinus tract usually forms. The prognosis for treatment of small lesions of internal root resorption is very good. If, however, the tooth structure is greatly weakened and perforation has occurred, the prognosis is poor and tooth extraction must be considered. Sodium hypochlorite, ultrasonic instrumentation and calcium hydroxide are the cornerstones of treatment of internal inflammatory root resorption. Mineral trioxide aggregate is being increasingly used as a root canal filling material, particularly in cases of perforation.