The incidence of Klinefelter Syndrome is 1 in 500 to 650 male births. It is thought that 1 out of 4 Klinefelter Syndrome males have a smaller than average penis, but who is going around measuring? However, an adult male’s erect penis that measures (SPL) 3.67 inches (9.32cm) or less is considered by reputable medical orgs to be an “adult” micropenis. This man’s erect penis is approx 3-1/4 inches (8.26cm) as shown. The most common sexual symptoms of XXY are small testes (aka balls) and infertility. Other symptoms can include impotence, ED, gynecomastia, learning disabilities, and low testosterone. XXY is not hereditary nor is it contagious nor is it curable.