Under normal conditions the male mammary glands do not undergo postnatal development and remain rudimentary throughout life. However, unilateral or bilateral enlargement of the male breast occasionally occurs in boys. This condition, called gyne-comastia,. is caused by a disturbed an-drogen-estrogen balance. Gynecomastia is frequently seen in hermaphrodites. Approximately 80% of males with Klinefelter syndrome show gyne-comastia.