Most infections of the male reproductive tract are sexually transmitted diseases (STDs). The most common STD in the United States is caused by the bacterium Chlamydia trachomatis, which, in males, mainly causes urethritis. This same organism also causes lymphogranuloma venereum, an STD associated with lymphadenopathy, which is rare in the United States. Both forms of these chlamydial infections respond to treatment with antibiotics.

Gonorrhea is caused by Neisseria gonorrhoeae, the gonococcus (GC). Infection usually centers in the urethra, causing urethritis with burning, a purulent discharge, and dysuria. Untreated, the disease can spread through the reproductive system. Gonorrhea is treated with antibiotics, but there has been rapid development of resistance to these drugs by gonococci.

Another common STD is herpes infection, caused by a virus. Mumps is a non–sexually transmitted viral disease that can infect the testes and lead to sterility. Other microorganisms can infect the reproductive tract as well, causing urethritis, prostatitis, orchitis, or epididymitis.

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