Migrant studies and studies examining the international variation of "latent" and clinical prostatic cancer imply that environmental factors play a prominent role in prostatic carcinogenesis. A strong familial tendency has been identified, but to what extent this is an effect of genetic factors has not been established. Hormones probably play an important role in the development of prostatic cancer, but it is not clear which hormones are critically involved, how they act and how they are influenced by genetic and environmental factors. The significance of sexual and occupational factors, benign prostatic hyperplasia and a history of vasectomy is also unclear. Overall, little is known about the factors responsible for the development of prostatic cancer and its progression to a clinically manifest form. Further understanding of the etiopathogenesis of prostate cancer could give rise to programmes for prevention and improve our ability to predict the behaviour of the individual tumour.