If your dog only has one testicle visible in the scrotum, the other one almost certainly didn’t fail to develop. It’s still inside his body, stuck somewhere along the path it was supposed to travel during puppyhood. This condition is called cryptorchidism, and it’s one of the most common developmental issues in male dogs. It’s not just a cosmetic quirk: that retained testicle carries real health risks, and understanding what happened helps you make the right call about treatment.
How Testicles Normally Descend
A male puppy’s testicles form near his kidneys while he’s still developing in the womb. Over the following weeks, a cord-like structure called the gubernaculum gradually shortens, pulling each testicle down through the abdomen and into the scrotum. This process typically wraps up by six to eight weeks of age.
Around six months, the inguinal canal (the passageway between the abdomen and the groin) closes. If a testicle hasn’t made it into the scrotum by then, it’s effectively locked in place. A vet may flag the issue as early as eight weeks if a testicle can’t be felt, but the official diagnosis is confirmed at six months once that window closes for good.
Why the Testicle Gets Stuck
The descent happens in two phases, and a problem in either one can leave a testicle stranded. In the first phase, hormones produced by the developing testicle trigger the gubernaculum to grow and form a bulb at its base, anchoring the testicle’s downward path. If hormonal signaling is off, the gubernaculum doesn’t develop properly, and the testicle stays high in the abdomen.
The second phase depends on testosterone guiding the testicle through the inguinal canal and into the scrotum. Abnormalities in hormone receptors, or in the physical connection between the testicle and its surrounding structures, can stall things partway. Some dogs end up with a testicle sitting in the abdomen; others have one lodged in the groin area, just short of the scrotum.
Genetics play a significant role. Cryptorchidism is a heritable trait, with heritability estimates ranging from 0.11 to 0.23 depending on the breed and study method. Researchers have identified specific gene variants linked to the condition, including one in a gene called HMGA2 on chromosome 10 that’s associated with inguinal cryptorchidism. Dogs carrying two copies of this variant have roughly 1.3 to 2.6 times the odds of being cryptorchid, depending on the comparison group.
Breeds at Higher Risk
Small breed dogs are about 2.7 times more likely to be cryptorchid than larger breeds. Boxers, Chihuahuas, Dachshunds, Maltese, Miniature Schnauzers, Pomeranians, Toy Poodles, Shetland Sheepdogs, and Yorkshire Terriers all show up more frequently in studies. That said, any breed can be affected.
Interestingly, research has found that matings between two dogs who have previously produced cryptorchid offspring tend to result in larger litter sizes. This may be one reason the trait persists in dog populations: the genes involved could offer a reproductive advantage in other ways, even as they increase the risk of retained testicles.
The Cancer Risk Is Significant
A retained testicle sits at a higher temperature than one in the scrotum, and that temperature difference has serious consequences. Cryptorchid testicles carry a 23 times greater risk of developing Sertoli cell tumors and a 16 times greater risk of seminomas compared to normally descended testicles. Both are types of testicular cancer.
Sertoli cell tumors are particularly concerning because they can produce estrogen, leading to signs like hair loss, a swollen prepuce, attraction from other male dogs, and in severe cases, bone marrow suppression. Seminomas tend to be less aggressive but still require surgical removal. Either type can develop silently inside the abdomen, where you won’t notice any swelling or changes the way you might with a scrotal tumor.
Torsion Is the Other Danger
A testicle sitting loose in the abdomen isn’t anchored the way a scrotal testicle is. It can twist on its blood supply, a painful emergency called testicular torsion. Dogs with torsion typically show sudden abdominal pain, vomiting, lethargy, loss of appetite, and difficulty walking. The spermatic cord and surrounding tissue rotate, cutting off blood flow. This requires emergency surgery.
Torsion is less common than cancer as a complication, but it tends to strike without warning and can become life-threatening quickly if the tissue dies.
How It’s Diagnosed
In most cases, your vet can diagnose cryptorchidism with a simple physical exam. If only one testicle is in the scrotum and the other can’t be felt in the groin area, the retained testicle is likely sitting somewhere in the abdomen. Ultrasound is the most common imaging tool used to locate it, helping the surgeon plan the approach before operating.
If your dog has been neutered and you’re unsure whether both testicles were removed (as sometimes happens with rescue dogs), a hormone stimulation test can determine whether any testicular tissue remains in the body.
Treatment Is Surgical
The standard treatment is neutering, which in a cryptorchid dog means removing both testicles: the normally descended one from the scrotum and the retained one from wherever it’s lodged. If the retained testicle is in the groin, it’s a relatively straightforward procedure. If it’s deep in the abdomen, the surgery is more involved, sometimes requiring a larger incision or laparoscopic approach.
Recovery takes about two weeks. Your dog will likely need an Elizabethan collar (the “cone of shame”) to keep him from licking the incision site, and activity should be restricted during healing. A follow-up appointment is typically scheduled two weeks after the operation to check the incision and confirm everything is healing well. Dogs that had abdominal surgery may need a slightly longer recovery period than those with a standard neuter.
Breeding a Cryptorchid Dog
A dog with one descended testicle can technically still reproduce, since that one testicle produces sperm. But breeding a cryptorchid dog is strongly discouraged by veterinarians and breed organizations. Because the condition is genetically inherited, affected dogs pass the risk to their offspring. Both the father and the mother contribute to the genetic picture, since females can carry the relevant gene variants without showing any outward signs.
Removing cryptorchid dogs from the breeding population is the primary way to reduce the condition’s prevalence. However, in breeds where cryptorchidism is especially common, eliminating every affected dog from breeding programs could reduce genetic diversity in ways that create other health problems. This is an ongoing challenge for breeders of predisposed breeds.