We evaluated 311 breast cancer patients admitted to Yong Dong Severance hospital Ibetween October 1st 1985 and July 31 th 1989, and were able to obtain the following conclusion. 1) there were 14(4.5%) bilateral breast cancers among the 311 confirmed breast cancers. 2) Among the bilateral breast cancers, 5(31%) were synchronous and 9(69%) metachronous. 3) Average interval between the first and the second breast cancer in metachronous cancers was 3.8years(1-15years). 4) Bilateral breast cancers was most prevalent in the fifth decade (6/14) with the mean age of 47 years. 5) Film mammogram and sonomammogram showed findings of typical breast malignancies. There was no additional specific finding for each cancer in bilateral breast cancers which was different from unilateral cancers. Therefore, in the patients with unilateral breast cancer, possibility of the second lesion in the contralateral side must be considered and a close follow-up observation should be done for at least 3 ye rs.