Prostate Cancer is the leading cancer in older men. when detected early (organ confined ), it is potentially curable by radical prostatectomy. Therefore, early detection is important and PSA is widely used for this purpose. It is considered one of the most promising tumour markers available PSA is an extremely useful tumour marker and is used to detect and monitor treatment of prostate cancer. Prior to introduction of testing for prostate specific antigen(PSA), two-thirds of prostate cancers were discovered after they were incurable. By this test, physicians / surgeons can now catch most prostate cancers before they spread beyond the prostate. PSA is produced by the prostate, a male sex gland about the size of a walnut that makes the fluid that carries sperms. Raised level of PSA normally is not found in a blood. In men with prostate disease, however, PSA levels in the blood may rise; two leading causes are: benign prostatic hyperplasia (BPH) and prostate cancer. PSA levels under 4 ng/ml are considered normal whereas above 10 ng/ml are cause for biopsy. In the “ diagnostic gray zone “, its levels between 4 and 10 ng/ml, the free PSA test can help differentiate between cancer and benign conditions such as BPH. PSA exists in multiple forms in the blood. Most of it remains bound to proteins, but some is free floating. In the early 1990 s, it was discovered that measuring the ratio of “ free to total “ PSA could further help in distinguishing prostate cancer from benign prostate disease.