Background: The distinction between radicular cysts and apical granulomas is important in treatment decision. Objectives: The current study aimed to differentiate these two lesions based on radiography images. Patients and Methods:The material consisted of 138 radiographs obtained using Kodak E -speed, in patients aged 29 to 47, divided into two groups: 109 granulomas and 29 radicular cysts. Size of radiography images was measured; the tooth then was extracted and examined in pathologist lab. The results were analyzed by SPSS.15 and ROC curve was created to find cut-off point to differentiate periapical granuloma and radicular cysts.