Internal resorption, a rare phenomenon, has been a quandary from the standpoints of both its diagnosis and treatment. It is usually asymptomatic and discovered by chance on routine radiographic examinations or by a classic clinical sign, "pink spot" in the crown. This paper emphasizes the etiology and pathophysiologic mechanisms involved in internal root resorption. Prognosis is good for smaller lesions; however, for those with extensive resorption associated with perforation the tooth structure is greatly weakened and the prognosis remains poor.