Dens evaginatus is a developmental anomaly characterized by the presence of an accessory cusp composed of enamel and dentine, usually containing pulp tissue. This condition is clinically important because of fracture or wear of the tubercle, which can frequently lead to the major complication of pulp necrosis and periapical infection. Treatment varies according to pulp condition, tubercle integrity, and stage of root development. Here we report a case of bilateral dens evaginatus with large periapical lesions. Non-surgical root canal treatment using calcium hydroxide medication was performed for both mandibular second premolars. At the 3-year postoperative recall examination, the teeth were asymptomatic and radiographically showed healing of the periapical lesions. (J Oral Sci 51, 475-479, 2009)