Large radicular lesions should be treated initially by orthograde root canal therapy. When the signs and symptoms of the infection (e.g. persistent purulent drainage) do not resolve after this treatment, then surgical approaches should be considered. In the cases of large radicular cysts, total enucleation of the cyst can endanger adjacent structures and teeth. Therefore, decompression or marsupialization techniques are recommended in order to decrease the size of the lesion. In this case report, a 55-year-old woman with previously initiated therapy was referred to endodontic department for management of a sinus tract associated with tooth #7. Root canal treatment was performed and intracanal irrigant (5.25% sodium hypochlorite) activated using passive ultrasonic application, various intracanal medicament (calcium hydroxide, double antibiotic paste) was used in multiple sessions, but intracanal purulent drainage was not resolved. After this, decompression was performed using needle cap to maintain the opening of the cyst and remained for three months. During this period the cavity was kept clean and rinsed by the patient with 0.2% chlorhexidine mouthwash. After three-year follow-up, radiographic examination revealed substantial osseous repair of the defect and clinical signs and symptoms were absent
