Associations between prostate cancer and dietary factors, physical activity and smoking were assessed based on data from a population-based case-control study. The study was conducted among residents of northeastern Ontario. Cases were identified from the Ontario Cancer Registry and diagnosed between 1995 and 1998 at ages 50 to 84 years (N=752). Male controls were identified from telephone listings and were frequency matched to cases on age (N=1,613). Logistic regression analyses investigated history of diet, physical activity and smoking as potential risk factors. Tomato intake had a significant positive association with prostate cancer risk for highest versus lowest quartiles (OR=1.6; 95 percent CI: 1.2-2.0). Associations were observed for tomato or vegetable juices and ketchup (OR=1.5; 95 percent CI: 1.2-1.9; OR=1.2; 95 percent CI: 1.0-1.5, respectively). Neither other dietary variables nor smoking were associated with prostate cancer risk. Strenuous physical activity by men in their early 50s was associated with reduced risk (OR=0.8; 95 percent CI: 0.6-0.9). While the recreational physical activity association was consistent with results from previous studies, the tomato products association was not.