The prostate is a part of the male reproductive system that helps make and store seminal fluid . In adult men, a typical prostate is about 3 centimeters long and weighs about 20 grams.  It is located in the pelvis , under the urinary bladder and in front of the rectum . The prostate surrounds part of the urethra , the tube that carries urine from the bladder during urination and semen during ejaculation .  Because of its location, prostate diseases often affect urination, ejaculation, and rarely defecation . The prostate contains many small glands which make about 20% of the fluid constituting semen .  In prostate cancer, the cells of these prostate glands mutate into cancer cells. The prostate glands require male hormones , known as androgens , to work properly. Androgens include testosterone , which is made in the testes ; dehydroepiandrosterone , made in the adrenal glands ; and dihydrotestosterone , which is converted from testosterone within the prostate itself. Androgens are also responsible for secondary sex characteristics such as facial hair and increased muscle mass.