What is the prostate? The prostate is a gland located in the lower urinary tract, under the bladder and around the urethra (Fig. 1). Only men have a prostate. It produces the fluid which carries semen. The prostate has smooth muscles which help to push out the semen during ejaculation. A healthy prostate is about the size of a large walnut and has a volume of 15-25 milli litres. The prostate slowly grows as men grow older.