This case report describes the endodontic treatment of a large cyst-like periradicular lesion using a combination of antibiotic drugs. A 15-yr-old boy with a large cyst-like lesion from the apices of his teeth 29 to 31. Conservative root canal treatment was performed (tooth #30). During treatment procedure, 2.5% sodium hypochlorite solution was used for irrigation and a combination of antibiotic drugs was used for the intracanal dressing. Periapical healing was observed 3-month after initial treatment and continued at the 7-month review.