In many countries of the world, prostate cancer is the second most common form of cancer in men, and in the United States it is now in first rank. It is an important public health problem, with > 0.25 million new cases diagnosed worldwide in the year 1985. Whereas earlier large increases in the incidence of prostate cancer were apparent throughout the world, the mortality rate has remained constant in generations of men born since the early years of this century. Most importantly, given that in several countries the increased number of children born after World War II will be in their mid-50s in the early part of the 21st century (at an age when cancer risk is becoming an important consideration), and coupled with the trends in increasing life expectancy, the consequence will be an increase in absolute terms in the number of cases of prostate cancer diagnosed. In the absence of treatment improvements and with prospects for prevention by modification of lifestyle remote within current knowledge, there will also be an increase in the number of deaths from prostate cancer worldwide. The situation would be further augmented by the presence of a temporal trend in risk that is widely reported from many countries and unlikely to be entirely artefact.