Finasteride is an alpha reductase inhibitor which has been used for some years to reduce the development of benign prostatic hypertrophy and alleviate some of its symptoms. This enzyme catalyses the conversion of testosterone to its bioactive dihydrotestosterone metabolite. Recently, a US trial of finasteride as a prophylactic against the develpment of prostate cacner has been closed. The Prostate Cancer Prevention Trial enrolled 18,882 men over 55 years (with normal DRE and PSA values of 3ng/ml or more) to 5mg finasteride per day or none. The trial was closed 15 months earlier than the proposed seven years because there was a 25% lower risk of developing the disease in the finasteride group. This is a potentialy important result One interesting and intriguing observation is that the tumours that occured in the finasteride group appeared to be of a higher grade than those occuring in the control group, albeit fewer of them. This may imply a less hormone responsive type of tumour. These results will be debated widely with regard to the possible prophylactic therapy in this disease.