The prostate is part of a man's sex organs. It's about the size of a walnut and surrounds the tube called the urethra, located just below the bladder. The urethra has two jobs: to carry urine from the bladder when you urinate and to carry semen during a sexual climax, or ejaculation. Semen is a combination of sperm plus fluid that the prostate adds. For men under 50, the most common prostate problem is prostatitis. For men over 50, the most common prostate problem is prostate enlargement. This condition is also called benign prostatic hyperplasia (BPH). Older men are at risk for prostate cancer as well, but this disease is much less common than BPH. This publication by the National Institutes of Health (Publication No. 08-4806) provides information about prostate problems such as prostatitis and enlargement (or BPH), diagnosis and treatments.