PURPOSE: To investigate the correlation between mammographic findings of infiltrating ductal carcinoma (IDC), patient age and pathologic grading. MATERIALS AND METHODS: The study included 103 cases of infiltrating ductal carcinoma in 102 women who during the preceding three years had undergone mammography and surgery. The mammograms were retrospectively reviewed by two radiologists. The mean age of the patients was 45.2 (range 26-74) years and the age distribution was seven in the 3rd decade, 37 in the 4th, 29 in the 5th, 24 in the 6th, and six in the 7th or above. Thirty-three lesions were histologic. Grade I, 59 were Grade II and 11 were Grade III. RESULTS: Ten (9.7%) of 103 cases, all of whom were younger than 50, were missed during mammographic diagnosis. On mammograms, primary findings of breast malignancy were found in 54 (74%) of 73 patients younger than 50 and 27 (90%) of 30 patients older than 51. Mass with or without microcalcification was found in 45 patients (62%) younger than 50 and in 26 (87%) older than 51. Nine (12%) and 3 (10%) in each age group showed secondary findings. There was no correlation between age distribution and histologic grading. Seventy-three percent of Grade I lesions and 78% of those of Grade III showed primary findings. Five lesions in each of Grade I and II were missed at mammographic interpretation, but this was not statistically significant (p=0.250). In all 11 Grade III cases, breast cancer were manifested as primary findings but this was not statistically significant (p=0.203). CONCLUSION: The majority of IDC were detected by mammography, but 9.7% of IDC patients, all younger than 50, were misdiagnosed. Most IDC was manifested as primary findings, particularly in patients aged over 51. There were no differences in pathlogic grading according to age distribution. All histologic Grade III lesions were detected by mammography.