Testicular torsion usually presents with sudden, severe, testicular pain (in groin and lower abdomen) and tenderness. There is often associated nausea and vomiting. The testis may be higher than its normal position. Mild pyrexia and redness of overlying area may be found.

Some of the symptoms are similar to epididymitis though epididymitis may be characterized by discoloration and swelling of the testis, often with fever, while the cremasteric reflex is usually present. Testicular torsion, or more probably impending testicular infarction, can also produce a low-grade fever.

There is often an absent or decreased cremasteric reflex.

This type of torsion is the most common cause of acute scrotal pain in boys ages 7–14. Its appearance is similar to that of testicular torsion but the onset of pain is more gradual. Palpation reveals a small firm nodule on the upper portion of the testis which displays a characteristic "blue dot sign". This is the appendix of the testis which has become discolored and is noticeably blue through the skin. Unlike other torsions, however, the cremasteric reflex is still active. Typical treatment involves the use of over-the-counter analgesics and the condition resolves within 2–3 days.

Polyorchidism is the incidence of more than two testicles. It is a very rare congenital disorder, with fewer than 201 cases reported in medical literature and 6 cases (two horses, two dogs and two cats) in veterinary literature.

Polyorchidism is generally diagnosed via an ultrasound examination of the testicles. However, the diagnosis of polyorchidism should include histological confirmation. The most common form is triorchidism, or tritestes, where three testicles are present. The condition is usually asymptomatic. A man who has polyorchidism is known as a polyorchid.

A hydrocele feels like a small fluid-filled balloon inside the scrotum. It is smooth, and is mainly in front of the testis. Hydroceles vary greatly in size and are typically painless and harmless. However, as the fluid continues to accumulate and the scrotum further enlarges, more discomfort can be expected. Large hydroceles will cause discomfort because of their size. Sometimes pain can be in both testicles as pressure from the enlarged area puts pressure against the unaffected area which can cause discomfort to the normal testicle. It has also been found to decrease a man's sex drive and makes him less active for fear of enlarging the mass. As the fluid of a hydrocele is transparent, light shone through the hydrocelic region will be visible from the other side. This phenomenon is called transillumination.

Symptoms of a hydrocele can easily be distinguished from testicular cancer, as a hydrocele is soft and fluid-filled, whereas testicular cancer feels hard and rough.

Many other less common conditions can lead to testicular pain. These include inguinal hernias, injury, hydroceles, and varicoceles among others. Testicular cancer is usually painless. Another potential cause is epididymal hypertension (also known as "blue balls").

An older system of classification structures polyorchidism into similar types, but with no subdivision between connected and disconnected testicles:

- Type 1: The testicle lacks an epididymis and vas deferens and has no connection to the other testicles.

- Type 2: The supernumerary testicle shares the epididymis and the vas deferens of the other testicles.

- Type 3: The supernumerary testicle has its own epididymis and shares a vas deferens.

- Type 4: Complete duplication of the testicle, epididymis and vas deferens.

Testicular torsion usually presents with an acute onset of diffuse testicular pain and tenderness of less than 6 hrs of duration. There is often an absent or decreased cremasteric reflex, the testicle is elevated, and often is horizontal. It occurs annually in about 1 in 4000 males before 25 years of age, is most frequent among adolescents ( 65% of cases presenting between 12 – 18 years of age ), and is rare after 35 years of age. Because it can lead to necrosis within a few hours, it is considered a surgical emergency. Another version of this condition is a chronic illness called intermittent testicular torsion (ITT) which is characterized by recurrent rapid acute onset of pain in one testis which will temporarily assume a horizontal or elevated position in the scrotum similar to that of a full torsion followed by eventual spontaneous detortion and rapid solution of pain. Nausea or vomiting may also occur.

A hydrocele testis is not generally thought to affect fertility. However, it may be indicative of other factors that may affect fertility.

This can be due to:

- One testicle not descending into the scrotum during normal embryonic or fetal development (3–4% of 'normal' live births), also known as undescended testis or cryptorchidism. In this case the testis is within the abdominal cavity, somewhere along the normal route of descent – most commonly, within the inguinal canal. Such a testis has an increased risk of malignancy.

- One testicle may disappear during development (the so-called vanishing testis) due to some intrauterine insult. This is thought to be most likely vascular, such as testicular torsion.

- One testicle may have been surgically removed through orchiectomy.

- One testicle may be injured.

Monorchism (also monorchidism) is the state of having only one testicle within the scrotum.

Because both the Wolffian ducts and Müllerian ducts begin to develop, the tissues are often intertwined, resulting in obstruction or nonpatency of the vas deferens or other parts of the reproductive excretory ducts. This can result in infertility, the most serious potential problem caused by this condition. Sometimes, transverse testicular ectopia is evident.

Cryptorchidism in AMH deficiency suggests that AMH may play a role in transabdominal testicular descent, perhaps by facilitating contraction of the gubernaculum.

Other Müllerian derivatives which may be present in at least a rudimentary form are the cervix, upper part of the vagina, and fallopian tubes.

The condition can come to attention because of a bulge in the inguinal canal of an XY infant due to herniation of the uterus. The presence of a uterus may be noticed if an ultrasound or MRI of the pelvis is performed to locate the testes or for other reasons. Occasionally the uterus is discovered during abdominal surgery for some other purpose in later childhood or adult life.

Although persistent Müllerian duct syndrome is classified as an intersex condition, it does not involve ambiguity or malformation of the external genitalia, which appear typical (apart from cryptorchidism if present). Sometimes the uterus enters a hernia. Sometimes the Müllerian structures get entangled with the spermatic ducts and interfere with the descent of the testes.

Apart from humans, this syndrome has been reported in dogs.

The varicoceles might be noticed as soft lumps, usually above the testicle and mostly on the left side of the scrotum. Right-sided and bilateral varicoceles do also occur. Some people who have them feel pain or heaviness in their scrotum. Varicoceles are sometimes discovered when investigating the cause of male infertility.

Patients with ovarian torsion often present with sudden onset of sharp and usually unilateral lower abdominal pain, in 70% of cases accompanied by nausea and vomiting.

Secondary hydroceles due to testicular diseases can be the result of cancer, trauma (such as a hernia), or orchitis (inflammation of testis), and can also occur in infants undergoing peritoneal dialysis. A hydrocele is not a cancer but it should be excluded clinically if a presence of a testicular tumor is suspected, however, there are no publications in the world literature that report a hydrocele in association with testicular cancer. Secondary hydrocele is most frequently associated with acute or chronic epididymo-orchitis. It is also seen with torsion of the testis and with some testicular tumors. A secondary hydrocele is usually lax and of moderate size: the underlying testis is palpable. A secondary hydrocele subsides when the primary lesion resolves.

- Acute/chronic epididymo-orchitis

- Torsion of testis

- Testicular tumor

- Hematocele

- Filarial hydrocele

- Post herniorrhaphy

- Hydrocele of an hernial sac

The swelling is soft and non-tender, large in size on examination, and the testis cannot usually be felt. The presence of fluid is demonstrated by trans illumination. These hydrocoeles can reach a huge size, containing large amount of fluid, as these are painless and are often ignored. They are otherwise asymptomatic, other than size and weight, causing inconvenience. However the long continued presence of large hydroceles causes atrophy of testis due to compression or by obstructing blood supply. In most cases, the hydrocele, when diagnosed early during complete physical examination, are small and the testis can easily be palpated within a lax hydrocele. However Ultrasound imaging is necessary to visualize the testis if the hydrocele sac is dense to reveal the primary abnormality. But these can become large in cases when left unattended. Hydroceles are usually painless, as are testicular tumors. A common method of diagnosing a hydrocele is by attempting to shine a strong light (transillumination) through the enlarged scrotum. A hydrocele will usually pass light, while a tumor will not (except in the case of a malignancy with reactive hydrocele).

The testicle or testis is the male reproductive gland in all animals, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testosterone. Testosterone release is controlled by the anterior pituitary luteinizing hormone; whereas sperm production is controlled both by the anterior pituitary follicle-stimulating hormone and gonadal testosterone.

Cryptorchidism is the absence of one or both testes from the scrotum. It is the most common birth defect of the male genital. About 3% of full-term and 30% of premature infant boys are born with at least one undescended testis. However, about 80% of cryptorchid testes descend by the first year of life (the majority within three months), making the true incidence of cryptorchidism around 1% overall. Cryptorchidism may develop after infancy, sometimes as late as young adulthood, but that is exceptional.

Cryptorchidism is distinct from monorchism, the condition of having only one testicle. The condition may occur on one or both sides; it more commonly affects the right testis.

A testis absent from the normal scrotal position may be:

1. anywhere along the "path of descent" from high in the posterior (retroperitoneal) abdomen, just below the kidney, to the inguinal ring;

2. in the inguinal canal;

3. "ectopic", having "wandered" from the path of descent, usually outside the inguinal canal and sometimes even under the skin of the thigh, the perineum, the opposite scrotum, or the femoral canal;

4. undeveloped ("hypoplastic") or severely abnormal ("dysgenetic");

5. missing (also see anorchia).

About two-thirds of cases without other abnormalities are unilateral; most of the other third involve both testes. In 90% of cases an undescended testis can be felt in the inguinal canal. In a small minority of cases missing testes may be found in the abdomen or appear to be nonexistent (truly "hidden").

Undescended testes are associated with reduced fertility, increased risk of testicular germ cell tumors and psychological problems when the boy is grown. Undescended testes are also more susceptible to testicular torsion (and subsequent infarction) and inguinal hernias. Without intervention, an undescended testicle will usually descend during the first year of life, but to reduce these risks, undescended testes can be brought into the scrotum in infancy by a surgical procedure called an orchiopexy.

Although cryptorchidism nearly always refers to "congenital" absence or maldescent, a testis observed in the scrotum in early infancy can occasionally "reascend" (move back up) into the inguinal canal. A testis which can readily move or be moved between the scrotum and canal is referred to as "retractile". The word is from the Greek "κρυπτός", "kryptos", meaning hidden "ὄρχις", "orchis", meaning testicle.

Cryptorchidism, hypospadias, testicular cancer and poor semen quality make up the syndrome known as testicular dysgenesis syndrome.

Many men who were born with undescended testes have reduced fertility, even after orchiopexy in infancy. The reduction with unilateral cryptorchidism is subtle, with a reported infertility rate of about 10%, compared with about 6% reported by the same study for the general population of adult men.

The fertility reduction after orchiopexy for bilateral cryptorchidism is more marked, about 38%, or 6 times that of the general population. The basis for the universal recommendation for early surgery is research showing degeneration of spermatogenic tissue and reduced spermatogonia counts after the second year of life in undescended testes. The degree to which this is prevented or improved by early orchiopexy is still uncertain.

Symptoms of orchitis are similar to those of testicular torsion. These can include:

- hematospermia (blood in the semen)

- hematuria (blood in the urine)

- severe pain

- visible swelling of a testicle or testicles and often the inguinal lymph nodes on the affected side.

Persistent Müllerian duct syndrome (PMDS) is the presence of Müllerian duct derivatives (fallopian tubes, uterus, and/or the upper part of the vagina) in what would be considered a genetically and otherwise physically normal male animal by typical human based standards. In humans, PMDS typically is due to an autosomal recessive congenital disorder and is considered by some to be a form of pseudohermaphroditism due to the presence of Müllerian derivatives.

Typical features include undescended testes (cryptorchidism) and the presence of a small, underdeveloped uterus in an XY infant or adult. This condition is usually caused by deficiency of fetal anti-Müllerian hormone (AMH) effect due to mutations of the gene for AMH or the anti-Müllerian hormone receptor, but may also be as a result of insensitivity to AMH of the target organ.

A varicocele is an abnormal enlargement of the pampiniform venous plexus in the scrotum. This plexus of veins drains blood from the testicles. The testicular blood vessels originate in the abdomen and course down through the inguinal canal as part of the spermatic cord on their way to the testis. Varicoceles occur in around 15% of all men.

Ovarian torsion (OT) is the rotation of the ovary at its to such a degree as to occlude the ovarian artery and/or vein.

Testicular enlargement is an unspecific sign of various testicular diseases, and can be defined as a testicular size of more than 5 cm (long axis) x 3 cm (short axis).

Blue balls is a slang term for a temporary fluid congestion in the testicles and prostate region caused by prolonged sexual arousal.

Testicular prostheses are available to mimic the appearance and feel of one or both testicles, when absent as from injury or as treatment in association to gender dysphoria. There have also been some instances of their implantation in dogs.

A testicular nubbin is the residual tissue of the human testis after a supposed perinatal vascular accident involving the testicular blood supply. The blood supply of the testis twists (called torsion) thereby cutting off the blood supply to the testis and results in testicular atrophy (shrinking). The nubbin is usually identified in childhood by the absence of a palpable testis in the scrotal sac. The tissue remnant usually includes fibrous tissue and signs of old infarction with hemosiderin deposition identified histologically. There is some disagreement as to whether these should be removed and whether there is a risk of future malignancy. They are typically removed surgically by pediatric urologists or pediatric general surgeons through either a scrotal or inguinal (or both) incision.

Orchitis is not rare in bulls and rams.

It has also been described in roosters.