PURPOSE: To evaluate the average glandular absorption radiation dose(AGARD) that results from tube voltage, target/filter material of the X-ray tube, enterance skin exposure, breast thickness and patterns in routine mammography. MATERIAL AND METHOD: After obtaining craniocaudal views of left breasts of 114 women, entrance skin exposure was measured by dosimetry. Under identical conditions of tube voltage and target/filter material of theX-ray tube, we obtained half value layer (HVL) and also calculated exposure-to-absorbed dose conversion factor(DgN) by Wu's methods. AGARD was calculated by entrance skin exposure multiplied by exposure-to-absorbed dose conversion factor. We analyzed AGARDs according to tube voltage, target/filter material, breast thickness and pattern using ANOVA method of the SPSS statistical packages. RESULT: Breast patterns were divided into 4 groups such as DY (n=72), P1 (n=1), P2 (n=10), and N1 (n=31), respectively. Their AGARDs were 161.5, 180, 172.8, and195.2 mrad respectively and showed no significant difference among groups. When divided by breast thickness into three groups, namely below 3cm, 3cm to 4.5cm, and above 4.5cm, the AGARD of each group was 178.3, 178.1, and 112.4mrad respectively and the last one was significantly low. Concerning the effect of tube voltages, AGARDs gradually decreased by increasing kVp. Furthermore, AGARD was lower when rhodium (Rh) rather than when molybdenum(Mo) was used as filter/target materials. CONCLUSION: There was no difference in AGARDs by breast pattern. Asmore increasing KvP or using Rh/Rh as the target/filter material of the X-ray tube, we reduced AGARD for the patient with dense or thick breasts.