Most of the time, a boy's testicles descend by the time he is 9 months old. Undescended testicles are common in infants who are born early. The problem occurs less in full-term infants. Some babies have a condition called retractile testes and the health care provider may not be able to find the testicles.

At what age is descent of the testes complete?

In many cases, the testes descend on their own into the scrotum by age 3 months. In most cases, the testes pass down by age 6 months without any treatment. In other cases, treatment may be needed.

How do you know if your balls haven't dropped?

The main sign: You can't see or feel the testicle in the scrotum. When both are undescended, the scrotum looks flat and smaller than you'd expect it to be. Some boys have what's called a retractile testicle. It may move up into their groin when they are cold or scared but moves back down on its own.