Epididymitis may be acute (symptoms last less than 6 weeks) or chronic (more than 3 months). Acute epididymitis is almost always unilateral. In sexually active men under 35 years of age, acute epididymitis is frequently caused by Chlamydia trachomatis and less frequently by Neisseria gonorrhoeae and is usually associated with overt or subclinical urethritis. Acute epididymitis in older men, children or following urinary tract instrumentation is commonly caused by gram-negative bacilli. The epididymis is sometimes the site of metastatic infection, such as tuberculosis. It is important to differentiate epididymitis from other causes for acute scrotum, such as testicular torsion and tumor. The cause of acute scrotum especially in children cannot always be identified. Therefore, Doppler ultrasonography and radionuclide scans are often used. In infants and young boys, genitourinary abnormalities are causative factors, and therefore should be excluded by imaging. Supportive measures and antimicrobial agents are the mainstay of therapy.