The most common cause of epididymitis is infection by bacteria. Bacteria in the urethra or bladder spread through the vas deferens, and into the epididymis.

Bacteria that cause epididymitis include:

• Sexually transmitted:
• Chlamydia in males
• Gonorrhea in males
• Bacteria from the intestine

Rare causes of epididymitis include:

• Viral infections, such as mumps
• Injury
• Medication side effects
• Amiodarone