In the prostate the enzyme 5alpha-reductase converts testosterone into more active form--dihydrotestosterone (DHT). This hormone strongly influences prostate function and takes part in its pathology Since the connection between androgens and pathology of this gland has been proved, pharmacological inhibition of conversion became one of the therapy strategies both for benign prostate hyperplasia and prostate cancer. Last decade has brought numerous, long term clinical trials which involved numerous men being administered finasteride and other 5alpha-reductase inhibitors in bening prostate hypertrophy (BPH) treatment and prostate cancer (PCa) prevention. The results confirmed main assumptions, however revealed complex androgens and other factors' activity overlapping with the effect of therapy on prostate disease.