I had a close male friend with Klinefelter's. He was taller than most, had less facial hair and was sterile. After reading the links provided here, this chromosomal abnormality is far from rare, ocuring in 1 out 500 males. Most not even aware that they have it. My dear friend had such issues with his condition. Sad...really sad.

Sex-chromosomal nondisjunction

Aneuploidy of sex chromosomes can also occur. The presence of extra X chromosome(s) causes Klinefelter syndrome in men and Triple X syndrome in women, while monosomy X (45, X) gives rise to women with Turner syndrome.

* XXX (Triple X syndrome)
* XXY (Klinefelter's syndrome)
* XYY (XYY syndrome)