Epididymitis (ep-ih-did-uh-MY-tis) is an inflammation of the coiled tube, called the epididymis, at the back of the testicle. The epididymis stores and carries sperm. Males of any age can get epididymitis. Epididymitis is most often caused by a bacterial infection, including sexually transmitted infections (STIs), such as gonorrhea or chlamydia. Sometimes, a testicle also becomes inflamed — a condition called epididymo-orchitis.