Epididymitis is an inflammation of the epididymis (the tubular structure that connects the testicle with the vas deferens).

Acute epididymitis causes swelling of the scrotum, pain in the testicles, and sometimes a fever of six weeks duration or less (usually with a gradual onset over several days).

If not treated, or in some other cases, the condition can become chronic. In chronic cases, there is usually no swelling, but simply pain.

The incidence is approximately 600,000 cases per year. The highest prevalence is in young men 19 to 35 years of age. The disorder is a major cause of hospital admissions in the military (causing approximately 20% of admissions).

Epididymitis is caused by spread of infection from the urethra or the bladder. The most common organisms involved in the condition in young heterosexual men are gonorrhoea and chlamydia. In children and older men, typical uropathogens, such as coliform oraganisms (E. coli), are much more common. This is also true in the case of homosexual men.

Mycobacterium tuberculosis (TB) can manifest also as epididymitis. "Beadlike" irregularities along vas deferens are the characteristic sign of this condition. Other bacteria (such as Ureaplasma) can also cause epididymitis.

A non-infectious cause of epididymitis is the use of anti-arrhythmic medication, amiodarone. Here, the inflammation is limited to the head of the epididymis and does not respond to anti-microbial therapy. The treatment is dosage reduction or change of medications.

An increased risk is associated with sexually active men who are not monogamous and do not use condoms. Men who have recently had surgery or have a history of structural problems involving the genito-urinary tract are also at increased risk (regardless of sexual behaviors). Other risk factors include chronic indwelling urethral catheter use and being uncircumcised.

Epididymitis may begin with a low grade fever and chills and a heavy sensation in the testicle. The testicle becomes increasingly sensitive to pressure or traction.

There may be lower abdominal discomfort or pelvic discomfort, and urination may cause burning or pain. On occasion, there may be a discharge from the urethra, blood in the semen, or pain on ejaculation. The testicle may enlarge significantly and produce severe pain.

It is important that this condition be distinguished from testicular torsion (a reduction or stoppage of the blood flow to the testicle) which requires emergency care. Testicular torsion is a surgical emergency and should be treated as soon as possible. Acute testicular pain should never be ignored.