The treatment of teeth associated with large periapical lesions require definitivě skill in diagnosis and decision making. In this čase report, a 41-year-old male with a large radiolucency in the periapical region of maxilla-ry right lateral incisor is described. The radiolucency resembled a periapical "bay cyst". The periapical lesion followed necrosis of the pulp. Non-surgical root canal treatment was doně. During the course of treatment sodium hypochlorite was ušed for irrigation and calcium hydroxide was ušed as the intracanal dressing. After obturation, the patient was instructed to come for evaluation, but he appeared only after 3 years. A radiograph taken at that time showed complete resolution of the lesion.

        Key words: large periapical radiolucencies of endodontic origin - root canal therapy - true cysts - bay cysts