A case of breast cancer in a patient with Klinefelter's syndrome is re
ported. Characteristic features of Klinefelter's syndrome include a 47
XXY karyotype and specific hormonal disorders. The risk of breast can
cer in patients with Klinefelter's syndrome is increased 66-fold as co
mpared with the general male population. This level of risk warrants r
outine screening for breast cancer.