The purpose of this study was to find out the relationship of radiographic lesion size, gender, age of patients and radiographic character to the diagnosis of periapical cyst and granuloma. The data was collected from 187 periapical lesions of 167 patients who undergone apical surgery at Department of Conservative Dentistry, Seoul National University Dental Hospital from 2003 to 2005. The lesion were surgically removed and send for biopsy to the Oral Pathology Laboratory. From the initial radiograph, lesion size was calculated using PiViewSTAR(R) (INFINITT, Korea) program. The obtained data were statistically evaluated using SPSS (p < 0.05). The result were as followings: 1. From 187 biopsy samples, the incidence of periapical cyst was 28.34% and granuloma was 65.24%. 2. There was a significant correlation between periapical cyst and the size of radiographic lesion (p < 0.01). 3. There were no significant correlations between age, gender, location of lesion and the final diagnosis (p > 0.05). 4. There was a significant correlation between the non-demarcation of the lesion and the incidence of periapical granuloma (p < 0.01).