Q. Our 1-month-old son has a problem I'm worried about.

Neither of his testicles is in his scrotum. His doctor says that we should just wait and see if they will come down naturally, but I've heard that there could be problems later in life if this condition persists.

Shouldn't something be done now?

A. Your son's problem is called an undescended testicle. Although this condition can lead to problems with fertility and cancer later in life, it's probably too soon to do anything about it yet.

About 3 percent of boys will have an undescended testicle at birth. Premature boys, or those with low birthweight -- under five pounds -- have an even higher rate of this condition -- as many as one in five. But most boys with this problem will have their testicles descend to their proper place in the scrotum by 1 to 3 months of age.

Fewer than one in 100 will still have this problem by the time they're 1 year old.

To understand how this problem can occur, it's helpful to understand how testicles normally develop. During the growth of the fetus, the testicles actually grow inside the abdomen, just above the kidneys.

As the fetus grows, the testicles migrate downward and eventually wind up in the scrotum about one month before birth.

In some babies, one or both testicles never reach the scrotum. They may stop short, at the top of the scrotum or just above the scrotum in the groin.

Many babies have what are known as "retractile" testicles, meaning that although they've reached their destined location in the scrotum, they have a tendency to retract back up into the groin, along the pathway of normal descent.

For young infants, most doctors will wait and see if the testicles complete their drop into the scrotum.

In fact, your doctor may ask you to examine your son from time to time to see if you find the testicles in the scrotum.

Sometimes, they will descend during a warm bath, only to retract when exposed to cool air, such as happens when you bring your baby to his doctor for an exam.

Males whose testicles never fully descend are at risk for two serious problems -- infertility and cancer of the testicle. There's some debate about whether treatment will reduce these risks, but most experts recommend treatment for a testicle that hasn't descended.

Some doctors use hormone treatments to trigger descent. In most cases, however, this treatment seems to work only for retractile testicles. In other words, hormone treatments just seem to speed up the descent of testicles that would normally descend anyway. They won't help children whose testicles are truly undescended. These children need surgery.

Surgery to bring the testicles into the scrotum is usually done before age 5. Many experts recommend that it be done after age 1 and before age 2. This range was chosen to maximize the chance of the testicles dropping by themselves and minimize the potential harm on future fertility.

However, if only one testicle is undescended, or even missing, most men will still be able to father children.

Some physicians feel that surgery doesn't decrease the risk of cancer in an undescended testicle, which runs about one in 10. But all authorities agree that surgery will aid in detecting a cancer should one develop in the future. For this reason, any boy who has had an operation for an undescended testicle should know how to examine himself to check for signs of cancer. They should look for any lumps, hardness or increase in size of the testicle.

Cancer of the testicle usually strikes men in their twenties and thirties. Boys with just one undescended testicle are at risk for cancer in both testicles, even the one that seemed to have developed normally.

This risk in the seemingly normal testicle, although much lower, may exist because of an underlying problem that not only makes one fail to descend but also makes both prone to develop cancer.

Surgery has some added benefits. It prevents the development of a groin hernia, or a condition known as torsion of the testicle. Torsion is a painful twisting of the blood vessels going to the testicle.

This condition, which usually strikes young boys, can lead to the death of the testicle. Both of these problems occur more frequently in boys with an undescended testicle.

Jay Siwek, a family physician from Georgetown University, practices at the Fort Lincoln Family Medicine Center and Providence Hospital in Northeast Washington. Consultation is a health education column and is not a substitute for medical advice from your physician.

Send questions to Consultation, Health Section, The Washington Post, 1150 15th St. NW, Washington, D.C. 20071. Questions cannot be answered individually.