PURPOSE: The purpose of this study is to evaluate mammographic findings of invasive ductal carcinoma(IDC) and invasive lobular carcinoma(ILC)and to find differential points between the two. MATERIALS AND METHODS: 239 patients, who underwent mammography prior to surgery and were proved to have IDC(224 patients) or ILC(15 patients)pathologically, were analized retrospectively. On mammogram, presence of mass and micro calcification were analized. When there was a mass on mammogram, lesion opacity was classified into high, equal, or low opacity andborder of the mass was classified into spiculated, poorly marginated, and well-marginated. When there was nodefinite mass, mammographic findings were classified into asymmetric opacity and no mass. RESULTS: Masses were observed in 168 patients(75%) of IDC and 12 patients(80%) of ILC. Border of the masses were spiculated(n=50,22.3%), poorly marginated(n=112, 50%), or well-marginated(n=6, 2.7%) in patients with IDC. Spiculated and poorly marginated borders were observed in 8 patients(53.3%) and 4 patients(26.7%) respectively, in patients with ILC. Microcalcifications were seen in 88 patients(39.3%) of IDC and 2 patients(13.3%) of ILC. Equal or low opacities ofthe lesions were observed in 29 patients(17.3%) of IDC and 5 patients(33.3%) of ILC. CONCLUSION: Although equalor low opacities were observed more frequently in ILC and microcalcifications were noted more frequently in IDC,it was difficult to differentiate the two diseases based on mammographic findings.