We evaluated 311 breast cancer patients admitted to Yong Dong Severance hospital between October 1st 1985 andJuly 31th 1989, and were able to obatin the following conclusions. 1) There were 14(4.5%) bilateral breast cancersamong 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 3.8 years(1-15 years). 4) Bilateral breast cancer was most prevalent in the fifth decade (6/14) with the mean age of47 years. 5) Film mammogram and sonomammogarm showed findings of typical breast malignancies. Therefore, in thepatients with unilateral breast cancer, possibility of the second lesion in the contralateral side must beconsidered and a close follow-up observation should be done for at least 3 years.