Many boys with Klinefelter syndrome have few noticeable symptoms, and the condition may go undiagnosed until adulthood. For others, the condition has a noticeable effect on growth or appearance. Klinefelter syndrome may also cause speech and learning problems in some boys.

Signs and symptoms of Klinefelter syndrome vary by age and may include:


  • Weak muscles
  • Slow motor development — taking longer than average to sit up, crawl and walk
  • Delay in speaking
  • Quiet, docile personality
  • Problems at birth, such as testicles that haven't descended into the scrotum

Boys and teenagers

  • Taller than average stature
  • Longer legs, shorter torso and broader hips compared with other boys
  • Absent, delayed or incomplete puberty
  • After puberty, less muscular bodies and less facial and body hair compared with other teens
  • Small, firm testicles
  • Small penis
  • Enlarged breast tissue (gynecomastia)
  • Weak bones
  • Low energy levels
  • Shyness
  • Difficulty expressing feelings or socializing
  • Problems with reading, writing, spelling or math
  • Attention problems


  • Infertility
  • Small testicles and penis
  • Taller than average stature
  • Weak bones
  • Decreased facial and body hair
  • Enlarged breast tissue
  • Decreased sex drive

When to see a doctor

See a doctor to rule out Klinefelter syndrome or another health condition if you or your son has:

  • Slow development during infancy or boyhood. If your son seems to be developing more slowly than other boys, see your son's doctor. Common signs and symptoms of Klinefelter syndrome include enlarged breast tissue (gynecomastia), small genitals, and small, firm testicles. Though some variation in physical and mental development is normal, it's best to check with a doctor if you have any concerns.

    Delays in growth and development can be the first sign of a number of conditions that need treatment — including Klinefelter syndrome. If your son does have Klinefelter syndrome, early treatment, including speech therapy, can help prevent or minimize problems.

  • Male infertility. If your partner hasn't gotten pregnant after a year of regular, unprotected sex, see a doctor. Infertility is usually caused by something other than Klinefelter syndrome, but many men aren't diagnosed with the condition until they realize they're unable to father a child.
June 25, 2013