The incidence of bladder cancer varies considerably among countries; the highest incidence rates are in Western communities. The variation in occurrence can partly be explained by differences in registration and coding practices of pTa tumours. Factors that modify the occurrence of bladder cancer are smoking and exposure to many kinds of carcinogenic substances in the workplace. Evidence also exists for radiotherapy to the pelvis, infection with Schistosoma haematobium, and certain medications as risk factors for bladder cancer. Despite enormous efforts, other important environmental or lifestyle factors that clearly and consistently increase or decrease the risk of bladder cancer have not been identified. Bladder cancer in first-degree relatives doubles the risk of bladder cancer; this increased risk might be due to high-penetrance susceptibility genes in a small subset of families, but most of this risk is probably caused by common lower-penetrance DNA variants that influence risk through one or more different cancer pathways. In the next 2 years genome-wide association scans will probably yield important new information on such variants. This might also facilitate new studies on lifestyle factors restricted to groups of susceptible people. In the future it will also be necessary to pay more attention to potential risk factors for different types of bladder cancer, more specifically low- vs high-grade cancer. The ultimate goal is to build a risk-prediction model by integrating environmental and genetic factors that can project individualized probabilities of developing bladder cancer.