Orchitis or infection of the testicles is not a rare disorder and infact is frequently seen in young males. The most common cause of orchitis is a virus infection. The virus that causes mumps has a great affinity for the testes and may affect either one of both testicles. About one-third of males who contract mumps after puberty develop orchitis. The disorder has been recognized since the time of Hippocrates. While the more common epididymo-orchitis is bacterial in origin, isolated orchitis usually has a viral etiology. Approximately 20% of prepubertal males with mumps develop orchitis. This viral disorder rarely occurs in post pubertal males with mumps.

Bacterial orchitis is even rarer and is usually associated with a concurrent epididymitis in the older males. In the old days, it was thought that every time the testes got infected, sterility resulted. This is false and infertility as a result of mumps is quite rare. For those lucky to live in countries where the mumps vaccine is available, mumps orchitis is rare, but in those countries without the vaccine, mumps orchitis is quite high. Asides from virus, orchitis can also be acquired from bacteria and in North America this is being increasingly recognized in the sexually transmitted disease (STD) clinics. The majority of bacteria are the ones which cause sexually transmitted disease. So the best way to avoid orchitis is to avoid sexual behavior that can cause STDs.