PURPOSE: To evaluate the mammographic and clinical features of bilateral breast cancer. MATERIALS AND METHODS: We retrospectively reviewed clinical records (n=23) and mammograms (n=15) of 23 patients with bilateral breast cancer. Patients' age, location of the tumor and pathologic staging were determined from clinical records. Mammographic features were classified as spiculated mass, nonspiculated mass, mass with microcalcification, microcalcification only, asymmetric density, and normal. RESULTS: Of the 23 cases of bilateral breast cancer, 8 (34.8%) were synchronous and 15 (65.2%) were metachronous. Age at diagnosis of cancer in the first breast was between 27 and 59 (mean 43) years; there was no statistically significant difference in mean age between patients with synchronous and metachronous cancer. The mean interval between the diagnosis of each lesion of themetachronous pairs was 9.1 years. In 11 of 23 cases (48%), tumors were located in the same quadrant, and in the other 12 cases (52%), they were in different quadrant. At mammography, five of 15 metachronous cancers (33%) were similar in appearance and 10 pairs (67%) were different. In 4 of 23 cases (17%), cancer in the first breast was at stage 0 and stage 1, and in 13 of 23 (57%), cancer in the second breast was at this same stage. CONCLUSION: In bilateral breast cancer, the two breasts frequently show different mammographic features. Cancer of the second breast was at an early stage; this suggest that regular examination and mammography are important and can allow early detection of contralateral breast cancer.