Dear Dr. Barchas,
Steve Seattle, AZ
Most likely, your dog has two testicles. However, only one of them is visible. The other testicle is “undescended,” meaning not in its proper place. Undescended testicles most commonly are located under the skin of the dog’s groin, although sometimes they are inside the abdomen. The syndrome occurs frequently in dogs. It is less common in cats.
Believe it or not, dealing with this situation is very important. Undescended testicles are dramatically more likely to develop cancer than their normal counterparts.
I recommend that you have a veterinarian assess your dog. He or she may be able to locate the missing testicle during a physical exam. Regardless of whether you wish to neuter your dog, the undescended testicle should be removed.