Prostate cancer is the most frequent cancer among Canadian men.  Unlike many other cancers (i.e. , lung, melanoma, etc) for which preventive measures can already be implemented, we are still completely empty-handed when it comes to prostate cancer.  Our team has just completed one of the largest epidemiologic studies (3,000 men) of factors that can increase the risk of prostate cancer, including a wide range of lifestyle factors (physical activity, diet, obesity, etc.).  For each subject, we also collected a detailed work history and biological specimens (saliva, toenail and hair samples).  Building on this massive existing infrastructure ($2 million), we are proposing to establish in Quebec a brand new collective and lasting effort in prostate cancer prevention by adding several new components to the base study.  These include accruing 1,000 more subjects to have stronger statistical strength, coding the occupational histories into 100 chemical exposures, coding the diet history into several suspected nutrients, assessing the role of air pollution, assessing the role of genetic susceptibility to environmental factors , and training a new generation of researchers in the area of prostate cancer prevention.