CONDITION
Cryptorchidism
Cryptorchidism describes the condition in which one or both testicles fail to descend fully into the scrotum. In dogs, the testicles normally move from their position near the kidneys down through the inguinal canal and into the scrotum during early development. When one testicle remains undescended, the condition is termed unilateral cryptorchidism; when both remain undescended, it is bilateral. Owners most commonly notice cryptorchidism when a puppy arrives for early vaccinations or neutering discussion, and the veterinary surgeon identifies that one or both testicles cannot be felt in the expected location. The retained testicle may be positioned in the abdomen or partway along the inguinal canal. Occasionally an owner may notice asymmetry in the scrotum, or a single firm structure where two would be expected. This page explores what can be observed on examination, the mechanisms underlying retained descent, how the condition is investigated when there is uncertainty, and the approaches taken to manage it over the animal's life. The discussion includes the implications for breeding, the differences between unilateral and bilateral presentations, and the factors that inform decisions about timing and method of surgical intervention.
Why this matters now
Cryptorchidism is recognised as a congenital condition, meaning the developmental sequence that leads to it begins before birth. In dogs, both testicles are typically palpable in the scrotum by six to eight weeks of age, and the condition is often identified during early puppy health checks or first vaccinations. Some clinicians may wait until around six months before confirming the diagnosis, as late descent occasionally occurs, though this is uncommon. Certain breeds, including toy and small breeds such as Toy Poodles, Pomeranians, Yorkshire Terriers and Chihuahuas, show higher rates of cryptorchidism, and the condition is heritable.
Once the window for natural descent has passed, a retained testicle will not move into the scrotum spontaneously. The testicle may remain in a stable position in the abdomen or inguinal canal for months or years without causing outward signs. Over time, the tissue of the retained testicle is exposed to the higher temperature of the body cavity, which can lead to degenerative changes and a progressive increase in the risk of tumour development, particularly from middle age onwards. The timeline and degree of risk vary between individuals, and some dogs live for years without obvious complications.
Signals & patterns
Early signals
One side of the scrotum appears empty
When examining a young male puppy, one half of the scrotum may look noticeably smaller or flatter than the other, or may feel soft with no firm structure inside. This asymmetry is often the first feature an owner or breeder notices.
Both sides of the scrotum feel empty
In bilateral cryptorchidism, the scrotum may appear underdeveloped or lack the usual fullness on both sides. This pattern is less common than unilateral retention but follows the same developmental mechanism.
A firm lump felt in the groin
In some cases, a retained testicle can be palpated as a small, mobile, firm mass under the skin of the inguinal region, partway along the normal path of descent. The lump is typically not painful and may move slightly when touched.
No discomfort or behavioural change
Young animals with cryptorchidism do not usually show pain, lethargy, or changes in appetite or behaviour. The absence of outward illness is characteristic in the early months and years.
Later signals
Swelling or firmness in the abdomen or groin
In older dogs, a retained testicle that undergoes tumour development may enlarge and become palpable as a firm mass in the abdomen or inguinal area. The mass itself may not cause pain initially, though discomfort can develop if the tumour grows large or affects surrounding structures.
Feminisation or changes in coat and behaviour
Certain tumours of retained testicles, particularly Sertoli cell tumours, can produce oestrogen. This may lead to symmetrical hair loss, enlargement of the nipples, attraction of other male dogs, or a pendulous prepuce. These signs reflect hormonal effects rather than local disease. Oestrogen excess can also suppress the bone marrow, causing anaemia and bleeding from a low platelet count. This cannot be judged at home and is found on blood tests. The outlook has historically been described as guarded to poor, and the marrow suppression can be fatal. In a 2022 series of 7 dogs treated with surgery and supportive care, all survived to discharge, 1 died within 4 weeks from worsening blood counts and 4 were alive after 1 year.
Sudden abdominal pain, vomiting or weakness
A retained testicle in the abdomen can twist on its blood supply, more often when a tumour has already changed it, which cuts off its blood flow. Reported signs are sudden abdominal pain, a stiff gait or reluctance to move, loss of appetite, vomiting, lethargy and sometimes fever or a swollen abdomen. A tumour that bleeds can cause similar signs with a swollen abdomen. The cause cannot be told apart at home. The longer the twist lasts, the more of the testicle dies, so vets treat torsion as a same-day surgical problem. Removing the testicle is usually curative if no tumour has spread.
Click to read about the biological mechanisms
How this is usually investigated
Diagnosis typically begins with careful palpation of the scrotum and inguinal region during routine examination. The history often reveals that one or both testicles have never been felt in the scrotum, or that a testicle previously palpable has become difficult to locate. When physical examination cannot confirm the position of a retained testicle, imaging may be used to identify its location and assess its size and appearance.
Physical examination
Abdominal ultrasound
Radiography
Computed tomography (CT)
Histopathology
Options & trade-offs
Management of cryptorchidism almost always involves surgical removal of the retained testicle, though the timing and extent of surgery can vary. Removing both testicles is the usual recommendation; a few owners choose to keep the descended testicle, although the condition is heritable and affected dogs are not used for breeding. The decision often balances the dog's age, the owner's breeding intentions, and the long-term cancer risk.
Surgical removal of the retained testicle (unilateral castration)
The retained testicle is located and removed through an abdominal or inguinal incision, depending on where it has arrested. The descended testicle, if present, may be left in place. This approach eliminates the cancer risk associated with the retained testicle while preserving fertility and some hormone production if the other testicle remains.
Trade-offs: Leaving the descended testicle intact means the dog remains fertile and could pass the heritable trait to offspring, so affected dogs are not used for breeding. The dog also continues to show male behaviours, which may not suit all households. The retained testicle must still be located and removed, which can involve more invasive surgery than routine castration if it lies deep in the abdomen.
Bilateral castration
Both testicles are removed in a single procedure, which may involve an abdominal approach for the retained testicle and a standard scrotal approach for the descended one. This is the most common approach and removes all testicular tissue, eliminating cancer risk, fertility, and testosterone-related behaviour.
Trade-offs: Bilateral castration is irreversible and removes all potential for breeding. Some owners prefer to delay surgery in young dogs to allow further skeletal and behavioural development, though this must be weighed against the increasing cancer risk over time.
Staged surgery
In some cases, surgery may be delayed or performed in stages, particularly if the dog is very young or if other health concerns need to be addressed first. Monitoring may continue for a period if there is uncertainty about whether descent might still occur, though this becomes less likely after a few months of age.
Trade-offs: Delaying surgery prolongs the period during which the retained testicle is exposed to higher temperatures and cancer risk accumulates. Staged approaches are less common and typically reserved for specific clinical or logistical circumstances.
Monitoring without surgery
A small number of owners choose not to pursue surgery, particularly in older dogs or those with other significant health conditions. The retained testicle is monitored periodically for changes in size or the development of systemic signs that might suggest tumour growth.
Trade-offs: Monitoring does not reduce cancer risk and the retained testicle may eventually develop a tumour that requires more complex surgery or produces hormonal effects. This approach is generally considered less suitable for younger dogs where the cumulative risk over a lifetime is substantial.
Common misconceptions
"The retained testicle will eventually descend on its own if given enough time."
Most testicles have reached the scrotum by around two months of age; descent after that is less likely and rarely happens after six months. The inguinal rings of most dogs close by around six months, after which the testicle can no longer pass through. Waiting beyond six months does not change the outcome but does allow more time for abnormal cellular changes to begin.
"A dog with one descended testicle is just as healthy as a normal dog and does not need surgery."
The descended testicle may function normally for hormone production and fertility, but the retained testicle carries a significantly elevated cancer risk that persists throughout the dog's life. The risk of tumour development increases with age, and some tumours produce hormones that can cause serious systemic illness.
"Cryptorchidism only affects pedigree dogs and is rare in mixed breeds."
Cryptorchidism occurs in both pedigree and mixed-breed dogs, though certain breeds show higher prevalence, suggesting a genetic component. The condition is heritable and affected dogs, regardless of breed, can pass the trait to offspring. Mixed-breed dogs are not immune to the condition.
Related conditions
Testicular Tumours
Testicular tumours develop far more frequently in retained testicles than in those that have descended normally, and dogs with cryptorchidism carry a substantially elevated risk of certain tumour types throughout life. The undescended testicle remains in a warmer environment than the scrotum provides, and this altered temperature may contribute to the increased likelihood of abnormal cell growth.
Sertoli Cell Tumour
Sertoli cell tumours are more common in retained testicles: about half are found in cryptorchid testicles. Two published studies put the risk of a testicular tumour of any type in cryptorchid dogs at about 9 and about 14 times that of dogs whose testicles have descended (relative risks of 9.2 and 13.6), and Sertoli cell tumours and seminomas are the types most often found. The hormonal changes that can accompany a Sertoli cell tumour may become apparent before the retained testicle itself is identified.
The page on this condition is being checked again and is offline for now.
Cryptorchidism often prompts broader reflection on inherited conditions and the long-term implications of breeding decisions. For households with young intact males, understanding the typical timeline of testicular descent and the reasons for early veterinary checks can be useful. The intersection of reproductive health, cancer risk, and surgical timing is a conversation that tends to evolve as the dog matures and as individual circumstances change.
Last reviewed: 10 October 2026 · Dr Alastair Greenway MRCVS